This is how skin, nails and hair work

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Last Medical Review: March 31, 2020
Medically Reviewed by Dr. Elisabeth Vincent Hamelin

The skin has several important tasks. For example, it protects our bodies against bacteria, viruses and the sun’s harmful radiation. The skin also helps us to maintain body temperature at a reasonable level. The skin also stores fat and fluid and prevents the body from drying out.

This text is about how the skin is structured and works. Here you can also read about the following:

  • Nails
  • hair
  • sebaceous glands
  • sweat glands.

This is how the skin is built up

The skin consists of several layers that are constructed in different ways. The skin can be divided into three parts:

  • epidermis
  • dermis
  • under the skin.

The epidermis protects the body

The epidermis is the outermost part of the skin, the part that is visible. It consists of flat cells that lie in several layers. The epidermis lacks blood vessels. Oxygen and nutrients are transported to the epidermis from the deeper layers of the skin, where the blood vessels are located.

The epidermis is different in thickness on different parts of the body

The epidermis is not as thick everywhere. It is 0.05 – 0.1 millimeters thick on most of the body. Skin that is very worn has thicker epidermis. It can, for example, be on the hands and on the underside of the feet. Under the foot, the epidermis may be 1 millimeter thick or more. The thinnest epidermis is on the eyelids.

The epidermal cells are renewed

The epidermal cells are located on a so-called basement membrane. On the basement membrane, the skin cells are tightly packed in several layers. The cells closest to the basement membrane often divide to replace cells that are worn on the surface of the epidermis. The newly formed cells are pushed upwards closer to the surface as they age.

The outermost part of the epidermis is called the horn layer

A so-called horn substance is stored in the cells that age in the epidermis. The horn substance makes the skin more resistant to, for example, corrosive substances and to the skin being worn and worn. The cells containing the horn substance are in the horn layer. It is the outermost layer of the epidermis. The horn layer also prevents the body from drying out. The horn layer becomes thicker if it is exposed to abrasion. Therefore, you can get whales on your hands after hard work. The horn substance is also called keratin.

The epidermis contains pigments that protect against the sun

The layers of cells closest to the basement membrane contain a dye or pigment. Those cells are called melanocytes. The pigment in the cells protects the skin from the sun’s harmful ultraviolet radiation. People with darker skin have more pigment cells than people with lighter skin.

More pigment is formed when the skin is exposed to sunlight

The skin darkens when the pigment cells are exposed to sunlight. It happens when you get tanned. This is because more pigment is formed to protect the body from the ultraviolet radiation. The amount of pigment is not always enough to protect the body. Then you can burn yourself. The skin becomes red, hot and burns where you have burned. Blisters may also form on the skin. You can also get sun damage, such as some forms of skin cancer.

The leather skin is strong and elastic

The leather skin lies under the epidermis. It is 0.5 – 3 millimeters thick. The leather skin is thickest on the back.

The leather skin consists of connective tissue, which contains much of the elastic fibers collagen and elastin. This makes the leather skin both strong and elastic. With age, the elastic fibers decrease, which makes the skin wrinkled and more limp. The elastic fibers can be damaged if exposed to sun. Therefore, you who sunbathe a lot can get skin that ages faster.

Here you can read more about connective tissue and other tissues.

Many blood vessels in the skin

There are many blood vessels in the leather skin. The blood vessels in the leather skin have several important tasks:

  • The blood vessels supply oxygen and nutrients to the skin.
  • The blood vessels carry away waste from the leather skin.
  • Blood flow helps the body maintain the right temperature.

The blood vessels contract when it is cold. This causes less blood to flow through the skin. Then the body retains more heat and the skin becomes pale. Similarly, the blood vessels expand when it is warm. Then the skin becomes redder as a lot of blood flows into the blood vessels. It causes heat to leave the body and cool the body.

The skin may also redden for other reasons, such as nervousness. Even then, the blood flow in the skin is changing.

The leather skin receives the impression of feeling

The leather skin includes lymph vessels, sensory bodies, nerves, hair follicles, sebaceous glands and sweat glands. Different types of sensory bodies respond to different sensory impressions such as touch, pressure, heat and cold. There are also nerve endings in the skin that respond to pain. The various signals of feeling are then transmitted to the brain through nerves.

Under the skin

Deeper in the skin, the leather skin transitions into the lower skin. There is no clear boundary between the leather skin and the subcutaneous skin.

The subcutaneous tissue contains many fat cells

The subcutaneous tissue consists, among other things, of porous connective tissue. The connective tissue contains a lot of fluid and therefore functions as a fluid supply. The subcutaneous tissue also consists of many fat cells. In a lean person, the subcutaneous skin is 2 – 10 millimeters thick. In a person who has a lot of fat in the body, the subcutaneous tissue can be up to ten centimeters thick. The adipose tissue in the subcutaneous skin is heat insulating and protects against shock. It is also an important energy reserve.

Nails

On the fingertips and toes, nails are formed from the cuticle. The cuticle lies in a fold of the epidermis. The cells in the cuticle split and then the nail grows. A fingernail grows about 1-2 millimeters a week. The toenails grow much slower.
Only the cells at the end of the cuticle live. The cells pushed forward contain horn substance, keratin. It makes them tough. Then a nail is formed. The nails protect the peaks of the fingers and toes.

Hair

Hair is often found everywhere on the skin except on the palms, soles of the feet, inner labia and penis. The hair on the head, in the armpits and around the genitals is longer and stronger than other hair. Even in some places on the face, the hair is longer and stronger than other hair, for example the hair of the eyebrows and eyelashes.

The head hair grows about a centimeter a month. A strand of hair on the head can remain for 2-8 years. Then it loosens and is replaced by a new strand of hair. While the hair is sitting on its head, it goes through three stages:

  • The first phase is the growth phase. Then the hair grows.
  • The second phase is the transition phase. Then the hair slowly stops growing.
  • The third phase is the rest phase. Then the hair has completely stopped growing and finally it comes off.

Every day you lose between 50 and 150 hairs.

The hair of young children and newborns

The fetus inside the uterus has thin soft hair all over the body. It’s called lanugo hair. Some newborns still have that hair when they are born. It usually falls off a few days after birth.

Some children are born with some hair on their heads while others have a lot. After a few weeks, the first hair falls off and is replaced with new, sometimes with a different color. Sometime after the age of two, the baby hair is replaced by slightly coarser hairs.

Then a strand of hair is formed

A strand of hair is formed in a similar way to a nail. There are so-called hair follicles in the leather skin. The hairs grow out of the hair follicles. This is done by dividing cells in the bottom of the hair follicle and pushing upwards. The cells contain horn substance, keratin, just like the cells of the nails. The horn substance makes the hair cells resistant. At the same time as the cells are pushed upwards in the hair follicle, they die. Most of the hair thus consists of dead cells.

The hair rises when you freeze

A small muscle sits next to the hair follicle. The muscle cannot be controlled by the will. The muscle contracts when you freeze or become scared. Then the hair rises and the skin becomes knotty. It is usually called that you get goose bumps.

Hair color and shape

The color of the hair depends on the pigment in the hair. In older people, the hair turns gray. This is because the hair cells form less or no pigment.

You get straight, curly or wavy hair depending on the type of hair your genetic parents have. The shape of the hair follicle affects the shape of the hair. The hair becomes straight if the hair follicle is straight, the hair becomes wavy or curly if the hair follicle is curved or helical. The sebaceous glands located near the hair follicle affect whether the hair is of a type that is fat or more dry.

Sebaceous glands

The sebaceous glands are found in the leather skin. They have an opening high up in the hair follicles or directly on the skin’s surface. The sebaceous glands form a fluid called sebum and which contains a lot of fat. Tallow follows the hairs up to the skin surface and makes it soft, supple and water resistant. Tallow contains substances that protect against bacteria.

There are most sebaceous glands on the face, scalp, middle of the chest and back. The sebaceous glands form the most sebum during puberty and are stimulated by male sex hormone. Acne is due to the opening of the sebaceous gland being blocked by sebum and the lower part of the sebaceous gland being inflamed.

Sweat glands

The sweat glands lie deep down in the leather skin or in the subcutaneous skin. They resemble a long, narrow tube that has been rolled up to form a tint. The sweat glands have an opening on the skin surface where the sweat empties.

Sweat contains water and salts

Sweat contains water and salts. You who sweat a lot may need to replace both the water and the salts that disappear from the body. Sweating helps the body keep the temperature at the right level. The body cools faster when you sweat.

The sweat from some glands has a special odor

Sweat glands are found everywhere on the body, but are most common in palms and soles of the feet. In the armpits, around the genitals and nipples and adjacent to the rectum there is a special kind of sweat glands. These sweat glands secrete lactic acid and urea. Therefore, the sweat gets a special odor when it is broken down by the bacteria of the skin.

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