Human skin

Human skin is the outer covering of our bodies and is the largest part of our integumentary system. It has layers that protect important parts of our bodies like muscles, bones, and internal organs. Human skin looks similar to the skin of most mammals and can be covered with hair or appear smooth.

Skin is very important because it helps keep us safe. It protects our bodies from harmful germs and helps stop us from losing too much water. Skin also helps control our temperature, gives us feeling, and makes vitamin D. When skin gets hurt, it can heal and sometimes forms a scar.

Different people have skin that looks different because of something called melanin. Some skin is dry, some is oily, and all skin types have many tiny living things called bacteria. These bacteria live on our skin and make each person's skin unique.

Structure

Human skin is very similar to the skin of other mammals, especially pigs. It has several layers that protect our muscles, bones, and internal organs. Skin helps protect the body from harm and also helps control temperature.

Skin is made up of three main layers: the epidermis, the dermis, and the subcutaneous tissue. The epidermis is the top layer that acts like a shield, keeping water in and harmful substances out. Beneath it, the dermis contains nerves, hair follicles, and glands. The subcutaneous tissue under the dermis helps connect the skin to muscles and bones and provides cushioning.

Cell count and cell mass

Skin cell table

This table shows the number of cells and their total weight for a healthy adult man who weighs about 70 kilograms. It includes information about the outer layer of skin, the deeper skin layers, hair follicles, and glands. The data comes from a scientific study about human cells.

Development

Skin colour

Human skin comes in many colours, from dark brown to light pinkish-white. This happened because of natural selection. The main reason for these colour differences is a substance called melanin, made in special cells in the skin. Melanin helps protect the skin from too much sunlight.

Other things that affect skin colour include carotene, which gives an orange colour, and hemoglobin in blood, which can make the skin look redder, especially when we are excited or exercising. Places closer to the equator usually have darker skin because there is more sunlight, while places farther away tend to have lighter skin.

Ageing

Further information: senescence

Further information: Intrinsic and extrinsic ageing

As skin gets older, it becomes thinner and harder to heal. It also loses some of its elasticity and may sag or wrinkle. This happens for many reasons, including less blood flow to the skin and lower activity in skin glands.

Photoageing

Main article: Photoageing

Too much sun can damage skin and increase the risk of skin cancer. Younger skin can heal from sun damage more quickly, but older skin heals more slowly, which can lead to more noticeable damage.

UV-induced DNA damage

Too much sunlight can harm the DNA in skin cells. Our bodies have ways to fix this damage, which helps protect against skin cancer.

Types

Most of our skin has tiny tubes that grow hair. Some parts, like our palms and the tops of our feet, are smooth and have no hair. There are two main kinds of skin: hairy skin, which has hair, and glabrous skin, which is smooth and hairless. The word "cutaneous" means something that belongs to the skin.

Functions

Skin is the body's largest organ and has many important jobs. It helps protect our insides from germs and damage. It also lets us feel things like heat, cold, and touch. Skin helps control our body temperature by letting heat in or out as needed.

Skin stops too much water from leaving our bodies and helps us stay dry. It also stores some water and fats and can make vitamin D when we are in the sun. Plus, skin helps us get rid of small amounts of waste through sweating. Some medicines can even be absorbed through the skin. Overall, skin keeps us safe, comfortable, and healthy.

Skin flora

Main article: Skin flora

Our skin is home to many tiny living things, like bacteria. Scientists have found many types of bacteria on human skin. These bacteria live in different areas of our skin. Researchers study these tiny living things to learn how they affect our health.

Clinical significance

Further information: Skin disease

The skin can also get sick. Problems like skin infections and skin neoplasms (which includes skin cancer) can happen. Doctors who study skin problems are called dermatologists, and they are a part of medicine.

Some illnesses can cause rashes on the skin. These rashes can help doctors understand someone's health. The top layer of skin, called the epidermis, can change. The skin can also show signs of other health problems, which is why doctors look closely at it. The colour of someone's skin can make it easier or harder to see these signs.

Society and culture

Hygiene and skin care

See also: Exfoliation (cosmetology)

The skin has tiny living things on it, like small plants and animals, that can't be washed away. There are so many of them that if you put all the tiny animals together, they would only take up as much space as a small pea. These tiny living things usually keep each other in balance and help keep the skin healthy. But sometimes, if something changes, like when certain medicines are used, they can grow too much and cause problems.

We should be careful when using beauty products on our skin because they can sometimes cause reactions. It's also important to wear the right clothes for the weather so our skin stays healthy. Sunlight, water, and air all help keep our skin in good shape.

Oily skin

Oily skin happens when special glands on the skin make too much of a natural substance that keeps the skin soft. Eating certain foods can make these glands work even more. Even though oily skin can sometimes cause shine and small bumps, it has its good points too—it often stays younger-looking for longer because the extra oil helps keep moisture in. However, oily skin can sometimes trap dirt and dead skin cells.

Permeability

Human skin does not let many outside substances pass through easily. The top layer, called the stratum corneum, acts like a shield to keep harmful particles out. This helps protect our body.

Scientists are studying tiny particles called nanoparticles to see how they move through the skin. Smaller particles, especially around 40 nanometers or less, can pass through the skin.

There are ways to help particles get through the skin more easily. For example, using ultraviolet radiation can slightly change the skin's surface. Other methods include using special tapes or applying certain chemicals. These methods are being explored for medical uses, like creating patches that can deliver medicine through the skin without a needle.

Sunblock and sunscreen are important products for protecting skin from the sun. Sunblock blocks most sun rays and usually does not need to be reapplied as often. Sunscreen also protects against sun rays but may need to be reapplied more frequently.

Eating certain foods like vitamins A, C, and E, as well as fruits, vegetables, whole grains, nuts, and seeds, can help keep skin healthy. These nutrients support the skin in many ways.