50 Fun Facts About Human Skin

Skin is the largest organ of the human body, making up roughly what share of body mass?

It weighs several kilograms and is the body's first line of defence.

Roughly how much surface area does the skin of an average adult cover?

That is about the size of a large bath towel or a small single bed.

What are the three primary layers of human skin, from outside in?

The hypodermis, or subcutaneous layer, is technically below the skin proper and holds much of the body's fat.

The prefix 'epi' in epidermis comes from Greek and means what?

The epidermis is the outermost layer and contains no blood vessels of its own.

How is the epidermis, which contains no blood vessels, mostly nourished?

Only its deepest cells get a small share from capillaries reaching up from below.

The stratum lucidum, an extra clear layer of the epidermis, is found only where on the body?

With this fifth layer, the skin there is known as 'thick skin'.

What is the outermost layer of the epidermis, made of about 15 layers of dead, flattened cells, called?

Most of the skin's barrier function lives in this cornified layer.

Which cell type makes up about 95 percent of the epidermis?

They are packed with the tough protein keratin, the same material as hair and nails.

Roughly how long does it take for the entire epidermis to be replaced by new cell growth?

A cell takes about two weeks to reach the granular layer and another four to cross the horny outer layer.

Where is the thinnest skin on the human body, at about 0.5 mm?

It is one of the first areas to show ageing, in the form of crow's feet.

The thickest skin on the body, about 4 mm, is found where?

The thick epidermis there makes the sweat glands coil into spirals.

The English word 'skin' is borrowed from Old Norse 'skinn', which originally meant what?

Its deeper Proto-Indo-European root means 'to cut', since hides were cut off to be worn.

The adjective 'cutaneous' comes from which Latin word for skin?

Cutis is also the technical name for the epidermis and dermis together.

According to one estimate, an average square inch of skin holds about how many sweat glands?

The same patch has around 20 blood vessels, 60,000 melanocytes and more than 1,000 nerve endings.

Roughly how many species of bacteria have been found living on human skin?

They come from 19 bacterial phyla, though four phyla account for almost all of them.

Which animal's skin so resembles ours in thickness, follicles and blood vessels that it is a research substitute?

Its dermal collagen and elastin content is also comparable to human skin.

The pigment melanin takes its name from a Greek word meaning what?

Its five basic types include eumelanin and the neuromelanin found in the brain.

Which form of melanin is largely responsible for the red or yellow tint of some skin and hair?

Human epidermis is roughly three-quarters eumelanin and one-quarter pheomelanin whatever the skin tone.

Melanin is made in a process called melanogenesis, which starts with the oxidation of which amino acid?

The reaction is followed by polymerisation inside organelles called melanosomes.

Melanocytes, the pigment-producing cells, sit in which layer of the epidermis?

They originate from neural crest cells and pass melanosomes to neighbouring surface cells.

Lightly and darkly pigmented skin differ in colour mainly because of what?

Both contain similar numbers of melanocytes; darker skin simply packs and distributes the pigment differently.

Freckles form not because there are more melanocytes but because existing ones do what?

UV-B exposure ramps up production, which is why freckles darken in summer.

Freckling is linked to rare variants of which gene, also associated with red hair?

Variants such as Arg151Cys and Arg160Trp are the most common in freckled people.

Strong evolutionary pressure for dark skin acted on early Homo about how long ago?

Losing body hair exposed folate in the blood to UV damage, favouring protective pigment.

The Fitzpatrick scale, developed in 1975, classifies human skin by what?

It runs from Type I, which always burns, to Type VI, which never burns.

Which nutrient does the skin synthesise for itself when exposed to ultraviolet B in sunlight?

For most people, skin synthesis provides more of it than food does.

What is the medical name for the reflex that produces goose bumps?

Tiny arrector pili muscles pull each hair upright; in furry animals this traps insulating air or makes them look bigger.

Which division of the nervous system triggers goose bumps as part of fight-or-flight?

Porcupines use the same reflex to raise their quills when threatened.

Which naturalist called blushing 'the most peculiar and most human of all expressions'?

He devoted a chapter of his 1872 book on the expression of emotions to it.

Fingerprint ridges form on a fetus at around what stage of pregnancy?

They remain unchanged until decomposition after death.

How do the fingerprints of identical twins compare?

Ridge patterns are shaped by conditions in the womb as well as genes.

Which Scottish surgeon in Tokyo published the first paper on fingerprint identification in 1880?

He also proposed recording them with printing ink.

Whose 1892 book 'Finger Prints' gave the first statistical model of fingerprint ID?

That same year an Argentine murder case became the first solved by a fingerprint, a bloody thumbprint of Francisca Rojas.

In what year did Scotland Yard begin fingerprinting individuals to identify criminals?

The Henry Classification System, developed in India, made large paper files searchable by ridge pattern.

The very rare condition of being born without any fingerprints is called what?

It has caused real problems for sufferers at border controls.

Which type of sweat gland is found almost all over the body and does most of the work of cooling?

The other main type is mostly confined to the armpits and groin, and its secretions feed odour-causing bacteria.

Ear-wax glands and milk glands are both modified versions of which type of sweat gland?

The ciliary glands of the eyelids are the third member of the family.

Sebaceous glands, which secrete oily sebum, are found on all parts of the skin except where?

They are densest on the face and scalp, and open into hair follicles.

Into which layer of the skin is tattoo ink deposited to make it permanent?

Ink placed only in the surface layer would be shed with the skin's regular turnover.

Ötzi the Iceman is the oldest known tattooed person. How many tattoos did he have?

Many sit over worn joints, prompting the theory that they were a form of acupuncture-like therapy.

Sunburn is an inflammatory response triggered by UV damage to what in skin cells?

Redness usually appears within hours, and full healing takes about a week.

Which Austrian chemist introduced the sun protection factor (SPF) rating in 1974?

His 1946 Gletscher Crème, the origin of Piz Buin, is thought to have had an SPF of just 2.

Red Vet Pet, forerunner of Coppertone, was developed in 1944 to protect whom from the sun?

Its inventor, airman Benjamin Green, named it for red veterinary petrolatum.

Which of the three main types of skin cancer is the most aggressive?

Skin cancer overall is the most commonly diagnosed cancer in humans.

Which two things never grow back inside scar tissue?

Scar collagen lines up in a single direction instead of the normal random basketweave, making it weaker.

What is the most effective medication for severe acne?

Doctors reserve it for severe cases because of its side effects; overgrowth of the bacterium Cutibacterium acnes is a common factor.

Dandruff affects roughly what share of adults?

It usually starts at puberty, is more common in men, and involves the yeast Malassezia.

The first great school of dermatology was established in 1708 at which Paris hospital?

The word 'dermatology' itself is first attested in English in 1819.

Calluses form in response to repeated friction; what forms instead if the friction is too much, too fast?

They are commonest on the feet, where pressure and rubbing are greatest.

Roughly what proportion of all human protein-coding genes are expressed in the skin?

Fewer than 100 genes are specific to skin alone, and those work in the epidermis.