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Human skin

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This article is about skin in humans. For other vertebrates, seeSkin.

Human skin
Skin of a human hand
Epidermis,dermis,andsubcutis,showing ahair follicle,gland,andsebaceous gland
Details
SystemIntegumentary system
Identifiers
Latincutis
TA98A16.0.00.002
TA27041
THH3.12.00.1.00001
FMA7163
Anatomical terminology

Thehuman skinis the outer covering of the body and is the largest organ of theintegumentary system.The skin has up to seven layers ofectodermaltissueguardingmuscles,bones,ligamentsandinternal organs.Human skin is similar to most of the othermammals' skin, and it is very similar topigskin. Though nearly all human skin is covered withhair follicles,it can appearhairless.There are two general types of skin: hairy andglabrous skin(hairless). The adjectivecutaneousliterally means "of the skin" (from Latincutis,skin).

Skin plays an importantimmunityrole in protecting the body againstpathogensand excessivewater loss.Its other functions areinsulation,temperature regulation,sensation, synthesis ofvitamin D,and the protection ofvitamin Bfolates. Severely damaged skin will try to heal by formingscar tissue.This is often discoloured and depigmented.

In humans,skin pigmentation(affected by melanin) varies among populations, and skin type can range fromdryto non-dry and fromoilyto non-oily. Such skin variety provides a rich and diverse habitat for the approximately one thousand species ofbacteriafrom nineteenphylawhich have been found on human skin.

Structure

[edit]
Layers, receptors, and appendages of human skin

Human skin shares anatomical, physiological, biochemical and immunological properties with other mammalian lines.Pig skinespecially shares similar epidermal and dermal thickness ratios to human skin: pig and human skin share similar hair follicle and blood vessel patterns; biochemically the dermal collagen and elastin content is similar in pig and human skin; and pig skin and human skin have similar physical responses to various growth factors.[1][2]

Skin hasmesodermalcells which producepigmentation,such asmelaninprovided bymelanocytes,which absorb some of the potentially dangerousultraviolet radiation(UV) insunlight.It containsDNA repairenzymesthat help reverse UV damage. People lacking thegenesfor these enzymes have high rates ofskin cancer.One form predominantly produced by UV light,malignantmelanoma,is particularly invasive, causing it tospreadquickly, and can often be deadly. Human skin pigmentation varies substantially between populations; this has led to the classification of people(s) on the basis ofskin colour.[3]

In terms of surface area, the skin is the second largest organ in the human body (the inside of the small intestine is 15 to 20 times larger). For the average adult human, the skin has a surface area of 1.5–2.0 square metres (15–20 sq ft). The thickness of the skin varies considerably over all parts of the body, and between men and women, and young and old. An example is the skin on the forearm, which is on average1.3 mmin males and1.26 mmin females.[4]One average square inch (6.5 cm2) of skin holds 650 sweat glands, 20 blood vessels, 60,000 melanocytes, and more than 1,000 nerve endings.[5][better source needed]The average human skin cell is about30 μmin diameter, but there are variants. A skin cell usually ranges from 25 to 40 μm2,depending on a variety of factors.

Skin is composed of three primary layers: theepidermis,thedermisand thehypodermis.[4]

Epidermis

[edit]
Main article:Epidermis

The epidermis, "epi" coming from theGreek languagemeaning "over" or "upon", is the outermost layer of the skin. It forms the waterproof, protective wrap over the body's surface, which also serves as a barrier toinfectionand is made up of stratified squamousepitheliumwith an underlyingbasal lamina.

The epidermis contains noblood vessels,and cells in the deepest layers are nourished almost exclusively by diffused oxygen from the surrounding air[6]and to a far lesser degree by blood capillaries extending to the outer layers of the dermis. The main type of cells that make up the epidermis areMerkel cells,keratinocytes,withmelanocytesandLangerhans cellsalso present. The epidermis can be further subdivided into the followingstrata(beginning with the outermost layer): corneum, lucidum (only in palms of hands and bottoms of feet), granulosum, spinosum, and basale. Cells are formed throughmitosisat the basale layer. The daughter cells (seecell division) move up the strata changing shape and composition as they die due to isolation from their blood source. The cytoplasm is released and the proteinkeratinis inserted. They eventually reach the corneum and slough off (desquamation). This process is called"keratinization".This keratinized layer of skin is responsible for keeping water in the body and keeping other harmful chemicals andpathogensout, making skin a natural barrier to infection.[7]

2D projection of a 3DOCT-tomogram of the skin at the fingertip, depicting thestratum corneum(≈500 μm thick) with the stratum disjunctum on top and thestratum lucidumin the middle. At the bottom are the superficial parts of the dermis. The sweat ducts are clearly visible. (See also:Rotating 3D Version)

The epidermis contains noblood vesselsand is nourished bydiffusionfrom the dermis. The main type of cells that make up the epidermis arekeratinocytes,melanocytes,Langerhans cells,andMerkel cells.The epidermis helps the skin regulate body temperature.

Layers

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The skin has up to seven layers of ectodermal tissue and guards the underlyingmuscles,bones,ligamentsandinternal organs.[8]The epidermis is divided into several layers, where cells are formed throughmitosisat the innermost layers. They move up the strata changing shape and composition as they differentiate and become filled withkeratin.After reaching the top layerstratum corneumthey are eventually 'sloughed off', ordesquamated.This process is calledkeratinizationand takes place within weeks.

It was previously believed that thestratum corneumwas "a simple, biologically inactive, outer epidermal layer comprising a fibrillar lattice of dead keratin".[9]It is now understood that this is not true, and that thestratum corneumshould be considered to be a live tissue.[10]While it is true that thestratum corneumis mainly composed of terminally differentiatedkeratinocytescalledcorneocytesthat are anucleated, these cells remain alive and metabolically functional untildesquamated.[citation needed]

Sublayers

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The epidermis is divided into the following 5 sublayers or strata:

Blood capillaries are found beneath the epidermis and are linked to an arteriole and a venule. Arterial shunt vessels may bypass the network in ears, the nose and fingertips.

Genes and proteins expressed in the epidermis

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About 70% of all human protein-coding genes are expressed in the skin.[11][12]Almost 500 genes have an elevated pattern of expression in the skin. There are fewer than 100 genes that are specific for the skin, and these are expressed in the epidermis.[13]An analysis of the corresponding proteins show that these are mainly expressed inkeratinocytesand have functions related tosquamousdifferentiation andcornification.

Dermis

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Main article:Dermis

The dermis is the layer of skin beneath theepidermisthat consists ofconnective tissueand cushions the body from stress and strain. The dermis is tightly connected to the epidermis by abasement membrane.It also harbours manynerve endingsthat provide the sense of touch and heat. It contains thehair follicles,sweat glands,sebaceous glands,apocrine glands,lymphatic vesselsandblood vessels.The blood vessels in the dermis provide nourishment and waste removal from its own cells as well as from the stratum basale of the epidermis.

The dermis is structurally divided into two areas: a superficial area adjacent to the epidermis, called thepapillary region,and a deep thicker area known as thereticular region.

Papillary region

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The papillary region is composed of looseareolar connective tissue.It is named for its finger-like projections calledpapillae,which extend toward the epidermis. The papillae provide the dermis with a "bumpy" surface that interdigitates with the epidermis, strengthening the connection between the two layers of skin.

In the palms, fingers, soles, and toes, the influence of the papillae projecting into the epidermis forms contours in the skin's surface. Theseepidermal ridgesoccur in patterns (see:fingerprint) that are genetically andepigeneticallydetermined and are therefore unique to the individual, making it possible to use fingerprints or footprints as a means ofidentification.

Reticular region

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The reticular region lies deep in the papillary region and is usually much thicker. It is composed of dense irregular connective tissue, and receives its name from the dense concentration ofcollagenous,elastic,andreticularfibres that weave throughout it. Theseproteinfibres give the dermis its properties of strength, extensibility, and elasticity.

Also located within the reticular region are theroots of the hairs,sebaceous glands,sweat glands,receptors,nails,and blood vessels.

Tattoo ink is held in the dermis.Stretch marks,often from pregnancy andobesity,are also located in the dermis.

Subcutaneous tissue

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Thesubcutaneous tissue(alsohypodermisandsubcutis) is not part of the skin, but lies below the dermis of thecutis.Its purpose is to attach the skin to underlying bone andmuscleas well as supplying it with blood vessels and nerves. It consists of loose connective tissue, adipose tissue andelastin.The main cell types arefibroblasts,macrophagesandadipocytes(subcutaneous tissue contains 50% of body fat). Fat serves as padding and insulation for the body.

Cross-section

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Skin layers, of both hairy and hairless skin

Cell count and cell mass

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Skin cell table

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The below table identifies the skin cell count and aggregate cell mass estimates for a 70 kg adult male (ICRP-23; ICRP-89, ICRP-110).[14][15][16]

Tissue mass is defined at 3.3 kg (ICRP-89, ICRP110) and addresses the skin's epidermis, dermis, hair follicles, and glands. The cell data is extracted from 'The Human Cell Count and Cell Size Distribution',[17][18]Tissue-Table tab in the Supporting Information SO1 Dataset (xlsx). The 1200 record Dataset is supported by extensive references for cell size, cell count, and aggregate cell mass.

Detailed data for below cell groups are further subdivided into all the cell types listed in the above sections and categorized by epidermal, dermal, hair follicle, and glandular subcategories in the dataset and on the dataset's graphical website interface.[19]While adipocytes in the hypodermal adipose tissue are treated separately in the ICRP tissue categories, fat content (minus cell-membrane-lipids) resident in the dermal layer (Table-105, ICRP-23) is addressed by the below interstitial-adipocytes in the dermal layer.

Named Tissue and

Associated Cell Groups

Cell Count Aggregate

Cell Mass (g)

Percent of

Total Mass

Skin Total 6.1E+11 846.7 100%
Adipocyte 7.3E+08 291.9 34.5%
Endothelial Cell (EnCs) 1.5E+10 6.16 0.7%
Epithelial Cells (EpC) 4.1E+11 313.9 37.1%
Eccrine Gland 1.7E+11 105 12.4%
Epidermal Keratinocytes 1.1E+11 85.5 10.1%
Hair Follicle 1.3E+11 119.9 14.2%
Mechanoreceptors 4.9E+09 3.6 0.4%
Epithelial Cells (EpC); Non-Nucleated 7.2E+10 28.2 3.3%
Fibroblasts 4.3E+10 94.6 11.2%
Myocytes 2.6E+07 0.08 0.01%
Neuroglia 8.5E+09 12.8 1.5%
Perivascular Cells / Pericytes / Mural 1.5E+09 0.56 0.07%
Stem Cells; Epithelial (EpSC) 3.6E+09 1.50 0.2%
White Blood Cells 5.4E+10 97.1 11.5%
Granulocytes (Mast Cell) 2.2E+10 32.6 3.8%
Lymphoid 1.3E+10 1.6 0.2%
Monocyte-Macrophage Series 1.9E+10 62.9 7.4%

Development

[edit]
Further information:Human embryogenesis § Integumentary system

Skin colour

[edit]
Main article:Human skin colour

Human skin shows high skin colour variety from the darkest brown to the lightest pinkish-white hues. Human skin shows higher variation in colour than any other single mammalian species and is the result ofnatural selection.Skin pigmentation in humans evolved to primarily regulate the amount ofultraviolet radiation(UVR) penetrating the skin, controlling its biochemical effects.[20]

The actual skin colour of different humans is affected by many substances, although the single most important substance determining human skin colour is the pigmentmelanin.Melanin is produced within the skin in cells calledmelanocytesand it is the main determinant of the skin colour ofdarker-skinnedhumans. The skin colour of people withlight skinis determined mainly by the bluish-white connective tissue under thedermisand by thehaemoglobincirculating in the veins of the dermis. The red colour underlying the skin becomes more visible, especially in the face, when, as consequence ofphysical exerciseor the stimulation of thenervous system(anger, fear),arteriolesdilate.[21]

There are at least five different pigments that determine the colour of the skin.[22][23]These pigments are present at different levels and places.

  • Melanin:It is brown in colour and present in thebasal layerof theepidermis.
  • Melanoid: It resembles melanin but is present diffusely throughout the epidermis.
  • Carotene:This pigment is yellow to orange in colour. It is present in the stratum corneum and fat cells of dermis andsuperficial fascia.
  • Hemoglobin(also spelledhaemoglobin): It is found in blood and is not a pigment of the skin but develops a purple colour.
  • Oxyhemoglobin: It is also found in blood and is not a pigment of the skin. It develops a red colour.

There is a correlation between the geographic distribution of UV radiation (UVR) and the distribution of indigenous skin pigmentation around the world. Areas that highlight higher amounts of UVR reflect darker-skinned populations, generally located nearer towards the equator. Areas that are far from the tropics and closer to the poles have lower concentration of UVR, which is reflected in lighter-skinned populations.[24]

In the same population it has been observed that adult humanfemalesare considerably lighter in skin pigmentation thanmales.Females need morecalciumduringpregnancyandlactation,andvitamin D,which is synthesized from sunlight, helps in absorbing calcium. For this reason it is thought that females may have evolved to have lighter skin in order to help their bodies absorb more calcium.[25]

TheFitzpatrick scale[26][27]is a numerical classification schema for human skin colour developed in 1975 as a way to classify the typical response of different types of skin to ultraviolet (UV) light:

I Always burns, never tans Pale, Fair, Freckles
II Usually burns, sometimes tans Fair
III May burn, usually tans Light Brown
IV Rarely burns, always tans Olive brown
V Moderate constitutional pigmentation Brown
VI Marked constitutional pigmentation Black

Ageing

[edit]
Further information:senescence
Further information:Intrinsic and extrinsic ageing
A typical rash
Skin infected withscabies

As skin ages, it becomes thinner and more easily damaged. Intensifying this effect is the decreasing ability of skin to heal itself as a person ages.

Among other things, skin ageing is noted by a decrease in volume and elasticity. There are manyinternal and external causesto skin ageing. For example, ageing skin receives less blood flow and lower glandular activity.

A validated comprehensive grading scale has categorized the clinical findings of skin ageing as laxity (sagging), rhytids (wrinkles), and the various facets of photoageing, includingerythema(redness), andtelangiectasia,dyspigmentation (brown discolouration), solar elastosis (yellowing), keratoses (abnormal growths) and poor texture.[28]

Cortisolcauses degradation ofcollagen,[29]accelerating skin ageing.[30]

Anti-ageing supplementsare used to treat skin ageing.[citation needed]

Photoageing

[edit]
Main article:Photoageing

Photoageing has two main concerns: an increased risk forskin cancerand the appearance of damaged skin. In younger skin, sun damage will heal faster since the cells in theepidermishave a faster turnover rate, while in the older population the skin becomes thinner and the epidermis turnover rate for cell repair is lower, which may result in thedermislayer being damaged.[31]

UV-induced DNA damage

[edit]

UV-irradiationof human skin cells generatesdamages in DNAthrough directphotochemical reactionsat adjacentthymineorcytosineresidues on the same strand of DNA.[32]Cyclobutanepyrimidine dimersformed by two adjacent thymine bases, or by two adjacent cytosine bases, in DNA are the most frequent types of DNA damage induced by UV. Humans, as well as other organisms, are capable of repairing such UV-induced damages by the process ofnucleotide excision repair.[32]In humans this repair process protects against skin cancer.[32]

Types

[edit]

Though most human skin is covered withhair follicles,some parts can behairless.There are two general types of skin, hairy andglabrous skin(hairless).[33]The adjectivecutaneousmeans "of the skin" (from Latincutis,skin).[34]

Functions

[edit]

Skin performs the following functions:

  1. Protection:an anatomical barrier from pathogens and damage between the internal and external environment in bodily defence;Langerhans cellsin the skin are part of theadaptive immune system.[7][35]Perspiration containslysozymethat break the bonds within the cell walls of bacteria.[36]
  2. Sensation:contains a variety of nerve endings that react toheat and cold,touch, pressure, vibration, and tissue injury; seesomatosensory systemandhaptics.
  3. Heat regulation:the skin contains a blood supply far greater than its requirements, which allows precise control of energy loss by radiation, convection and conduction. Dilated blood vessels increase perfusion and heat loss, while constricted vessels greatly reduce cutaneous blood flow and conserve heat.
  4. Control of evaporation:the skin provides a relatively dry and semi-impermeable barrier to fluid loss.[35]Loss of this function contributes to the massive fluid loss inburns.
  5. Aesthetics and communication:others see our skin and can assess our mood, physical state and attractiveness.
  6. Storage and synthesis:acts as a storage centre for lipids and water, as well as a means of synthesis ofvitamin Dby action ofUVon certain parts of the skin.
  7. Excretion:sweatcontainsurea,however its concentration is 1/130th that ofurine,henceexcretionby sweating is at most a secondary function to temperature regulation.
  8. Absorption:the cells comprising the outermost 0.25–0.40 mm of the skin are "almost exclusively supplied by external oxygen", although the "contribution to total respiration is negligible".[6]In addition, medicine can be administered through the skin, by ointments or by means of adhesivepatch,such as thenicotine patchoriontophoresis.The skin is an important site of transport in many other organisms.
  9. Water resistance:The skin acts as a water-resistant barrier so essential nutrients are not washed out of the body.[35]

Skin flora

[edit]
Main article:Skin flora

The human skin is a rich environment for microbes.[37][38]Around 1,000 species ofbacteriafrom 19 bacterialphylahave been found.[38][37]Most come from only four phyla:Actinomycetota(51.8%),Bacillota(24.4%),Pseudomonadota(16.5%), andBacteroidota(6.3%).PropionibacteriaandStaphylococcispecies were the main species insebaceousareas. There are three main ecological areas: moist, dry and sebaceous. In moist places on the bodyCorynebacteriatogether withStaphylococcidominate. In dry areas, there is a mixture of species but dominated byBetaproteobacteriaandFlavobacteriales.Ecologically, sebaceous areas had greater species richness than moist and dry ones. The areas with least similarity between people in species were the spaces betweenfingers,the spaces betweentoes,axillae,andumbilical cordstump. Most similarly were beside thenostril,nares(inside the nostril), and on the back.

Reflecting upon the diversity of the human skin researchers on the human skinmicrobiomehave observed: "hairy, moist underarms lie a short distance from smooth dry forearms, but these two niches are likely as ecologically dissimilar as rainforests are to deserts."[37]

TheNIHconducted theHuman Microbiome Projectto characterize the human microbiota, which includes that on the skin and the role of this microbiome in health and disease.[39]

Microorganisms likeStaphylococcusepidermidiscolonize the skin surface. The density of skin flora depends on region of the skin. The disinfected skin surface gets recolonized from bacteria residing in the deeper areas of the hair follicle, gut and urogenital openings.

Clinical significance

[edit]
Further information:skin disease

Diseases of the skin includeskin infectionsandskin neoplasms(including skin cancer).Dermatologyis the branch ofmedicinethat deals with conditions of the skin.[33]

There are seven cervical, twelve thoracic, five lumbar, and five sacral.[clarification needed]Certain diseases like shingles, caused by varicella-zoster infection, have pain sensations and eruptive rashes involving dermatomal distribution. Dermatomes are helpful in the diagnosis of vertebral spinal injury levels. Aside from the dermatomes, the epidermis cells are susceptible to neoplastic changes, resulting in various cancer types.[40]

The skin is also valuable for diagnosis of other conditions, since manymedical signsshow through the skin.Skin coloraffects the visibility of these signs, a source of misdiagnosis in unaware medical personnel.[41][42]

Society and culture

[edit]

Hygiene and skin care

[edit]
See also:Exfoliation (cosmetology)

The skin supports its ownecosystemsofmicroorganisms,includingyeastsand bacteria, which cannot be removed by any amount of cleaning. Estimates place the number of individual bacteria on the surface of human skin at 7.8 million per square centimetre (50 million per square inch), though this figure varies greatly over the average 1.9 square metres (20 sq ft) of human skin. Oily surfaces, such as the face, may contain over 78 million bacteria per square centimetre (500 million per square inch). Despite these vast quantities, all of the bacteria found on the skin's surface would fit into a volume the size of a pea.[43]In general, the microorganisms keep one another in check and are part of a healthy skin. When the balance is disturbed, there may be an overgrowth and infection, such as whenantibioticskillmicrobes,resulting in an overgrowth of yeast. The skin is continuous with the innerepitheliallining of the body at the orifices, each of which supports its own complement of microbes.

Cosmetics should be used carefully on the skin because these may cause allergic reactions. Each season requires suitable clothing in order to facilitate the evaporation of the sweat. Sunlight, water and air play an important role in keeping the skin healthy.

Oily skin

[edit]

Oily skin is caused by over-active sebaceous glands, that produce a substance calledsebum,a naturally healthy skin lubricant.[8][44]A highglycemic-indexdiet anddairy products(except for cheese) consumption increaseIGF-1generation, which in turn increases sebum production.[44]Overwashing the skin does not cause sebum overproduction but may cause dryness.[44]

When the skin produces excessivesebum,it becomes heavy and thick in texture, known as oily skin.[44]Oily skin is typified by shininess, blemishes andpimples.[8]The oily-skin type is not necessarily bad, since such skin is less prone to wrinkling, or other signs of ageing,[8]because the oil helps to keep needed moisture locked into theepidermis(outermost layer of skin). The negative aspect of the oily-skin type is that oily complexions are especially susceptible to clogged pores,blackheads,and buildup of dead skin cells on the surface of the skin.[8]Oily skin can besallowand rough in texture and tends to have large, clearly visible pores everywhere, except around the eyes and neck.[8]

Permeability

[edit]

Human skin has a lowpermeability;that is, most foreign substances are unable to penetrate and diffuse through the skin. Skin's outermost layer, the stratum corneum, is an effective barrier to mostinorganicnanosized particles.[45][46]This protects the body from external particles such as toxins by not allowing them to come into contact with internal tissues. However, in some cases it is desirable to allow particles entry to the body through the skin. Potential medical applications of such particle transfer has prompted developments innanomedicineandbiologyto increase skin permeability. One application of transcutaneous particle delivery could be to locate and treat cancer. Nanomedical researchers seek to target the epidermis and other layers of active cell division wherenanoparticlescan interact directly with cells that have lost their growth-control mechanisms (cancer cells). Such direct interaction could be used to more accurately diagnose properties of specific tumours or to treat them by delivering drugs with cellular specificity.

Nanoparticles

[edit]

Nanoparticles 40 nm in diameter and smaller have been successful in penetrating the skin.[47][48][49]Research confirms that nanoparticles larger than 40 nm do not penetrate the skin past the stratum corneum.[47]Most particles that do penetrate will diffuse through skin cells, but some will travel downhair folliclesand reach the dermis layer.

The permeability of skin relative to different shapes of nanoparticles has also been studied. Research has shown that spherical particles have a better ability to penetrate the skin compared tooblong(ellipsoidal) particles because spheres are symmetric in all three spatial dimensions.[49]One study compared the two shapes and recorded data that showed spherical particles located deep in the epidermis and dermis whereas ellipsoidal particles were mainly found in the stratum corneum and epidermal layers.[49]Nanorodsare used in experiments because of their uniquefluorescentproperties but have shown mediocre penetration.

Nanoparticles of different materials have shown skin's permeability limitations. In many experiments, gold nanoparticles 40 nm in diameter or smaller are used and have shown to penetrate to the epidermis.Titanium oxide(TiO2),zinc oxide(ZnO), andsilver nanoparticlesare ineffective in penetrating the skin past the stratum corneum.[46][50]Cadmium selenide(CdSe)quantum dotshave proven to penetrate very effectively when they have certain properties. Because CdSe is toxic to living organisms, the particle must be covered in a surface group. An experiment comparing the permeability of quantum dots coated inpolyethylene glycol(PEG), PEG-amine,andcarboxylic acidconcluded the PEG and PEG-amine surface groups allowed for the greatest penetration of particles. The carboxylic acid coated particles did not penetrate past the stratum corneum.[49]

Increasing permeability

[edit]

Scientists previously believed that the skin was an effective barrier to inorganic particles. Damage from mechanical stressors was believed to be the only way to increase its permeability.[51]

Recently, simpler and more effective methods for increasing skin permeability have been developed.Ultraviolet radiation(UVR)slightly damages the surface of skin and causes a time-dependent defect allowing easier penetration of nanoparticles.[52]The UVR's high energy causes a restructuring of cells, weakening the boundary between the stratum corneum and the epidermal layer.[52][51]The damage of the skin is typically measured by thetransepidermal water loss(TEWL), though it may take 3–5 days for the TEWL to reach its peak value. When the TEWL reaches its highest value, the maximum density of nanoparticles is able to permeate the skin. While the effect of increased permeability after UVR exposure can lead to an increase in the number of particles that permeate the skin, the specific permeability of skin after UVR exposure relative to particles of different sizes and materials has not been determined.[52]

There are other methods to increase nanoparticle penetration by skin damage:tape strippingis the process in which tape is applied to skin then lifted to remove the top layer of skin;skin abrasionis done by shaving the top 5–10 μm off the surface of the skin;chemical enhancementapplies chemicals such aspolyvinylpyrrolidone(PVP),dimethyl sulfoxide(DMSO), andoleic acidto the surface of the skin to increase permeability;[53][54]electroporationincreases skin permeability by the application of short pulses ofelectric fields.The pulses are high voltage and on the order of milliseconds when applied.Charged moleculespenetrate the skin more frequently than neutral molecules after the skin has been exposed to electric field pulses. Results have shown molecules on the order of 100 μm to easily permeate electroporated skin.[54]

Applications

[edit]

A large area of interest in nanomedicine is thetransdermal patchbecause of the possibility of a painless application of therapeutic agents with very few side effects. Transdermal patches have been limited to administer a small number of drugs, such asnicotine,because of the limitations in permeability of the skin. Development of techniques that increase skin permeability has led to more drugs that can be applied via transdermal patches and more options for patients.[54]

Increasing the permeability of skin allows nanoparticles to penetrate and targetcancercells. Nanoparticles along withmulti-modal imagingtechniques have been used as a way to diagnose cancernon-invasively.Skin with high permeability allowed quantum dots with anantibodyattached to the surface for active targeting to successfully penetrate and identify canceroustumoursin mice. Tumour targeting is beneficial because the particles can be excited usingfluorescence microscopyand emit light energy and heat that will destroy cancer cells.[55]

Sunblock and sunscreen

[edit]

Sunblock and sunscreen are different important skin-care products though both offer full protection from the sun.[56]

Sunblock—Sunblockis opaque and stronger than sunscreen, since it is able to block most of theUVA/UVB raysand radiation from the sun, and does not need to be reapplied several times in a day. Titanium dioxide and zinc oxide are two of the important ingredients in sunblock.[57]

Sunscreen—Sunscreenis more transparent once applied to the skin and also has the ability to protect against UVA/UVB rays, although the sunscreen's ingredients have the ability to break down at a faster rate once exposed to sunlight, and some of the radiation is able to penetrate to the skin. In order for sunscreen to be more effective it is necessary to consistently reapply and use one with a higher sun protection factor.

Diet

[edit]

Vitamin A,also known asretinoids,benefits the skin by normalizingkeratinization,downregulatingsebumproduction, which contributes toacne,and reversing and treating photodamage, striae, andcellulite.

Vitamin Dand analogues are used to downregulate the cutaneous immune system and epithelial proliferation while promoting differentiation.

Vitamin Cis anantioxidantthat regulates collagen synthesis, forms barrier lipids, regenerates vitamin E, and provides photoprotection.

Vitamin Eis a membrane antioxidant that protects against oxidative damage and also provides protection against harmfulUVrays. [58]

Several scientific studies confirmed that changes in baseline nutritional status affects skin condition. [59]

Mayo Cliniclists foods they state help the skin: fruits and vegetables, whole-grains, dark leafy greens, nuts, and seeds.[60]

See also

[edit]

References

[edit]
  1. ^Herron AJ (5 December 2009)."Pigs as Dermatologic Models of Human Skin Disease"(PDF).ivis.org.DVM Center for Comparative Medicine and Department of Pathology Baylor College of Medicine Houston, Texas.Retrieved27 January2018.pig skin has been shown to be the most similar to human skin. Pig skin is structurally similar to human epidermal thickness and dermal-epidermal thickness ratios. Pigs and humans have similar hair follicle and blood vessel patterns in the skin. Biochemically pigs contain dermal collagen and elastic content that is more similar to humans than other laboratory animals. Finally pigs have similar physical and molecular responses to various growth factors.
  2. ^Liu J, Kim D, Brown L, Madsen T, Bouchard GF."Comparison of Human, Porcine and Rodent Wound Healing With New Miniature Swine Study Data"(PDF).sinclairresearch.Sinclair Research Centre, Auxvasse, MO, USA; Veterinary Medical Diagnostic Laboratory, Columbia, MO, USA. Archived fromthe original(PDF)on 27 January 2018.Retrieved27 January2018.Pig skin is anatomically, physiologically, biochemically and immunologically similar to human skin
  3. ^Maton A, Hopkins J, McLaughlin CW, Johnson S, Warner MQ, LaHart D, Wright JD (1893).Human Biology and Health.Englewood Cliffs, New Jersey, USA: Prentice Hall.ISBN978-0-13-981176-0.
  4. ^abWilkinson PF, Millington R (2009).Skin(Digitally printed version ed.). Cambridge: Cambridge University Press. pp. 49–50.ISBN978-0-521-10681-8.
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