The skin

The skin is the largest organ in the body. Find out about the layers and cells of the skin, and how skin works.

What the skin does

Melanoma is a cancer that usually starts in the skin.

The different things the skin does include:

  • protecting the body from injury
  • protecting the body from the harmful effects of ultraviolet (UV) light
  • keeping bacteria or viruses from getting into the blood and causing infections
  • keeping fluids and proteins in the body
  • controlling the body’s temperature
  • giving us our sense of touch, through nerve endings, to feel and react to pain, heat or pressure
  • helping the body make vitamin D (when skin is exposed to the sun) which is important to keep our bones healthy
  • providing the skin with its colour.

Layers of the skin

The skin has different layers. There are 2 main layers that cover a fatty layer underneath.

The epidermis

This is the thin outer layer of the skin. The epidermis contains 3 types of cell:

  • squamous cells – flat cells on the surface of the skin that are always shedding
  • basal cells – rounder cells that are found under the squamous cells
  • melanocytes – the cells that melanoma starts from, found in between the basal cells.

The dermis

This is the inner layer of skin and is much thicker than the epidermis. It contains nerve endings, blood vessels, sweat glands and lymphatic vessels. It provides the epidermis with nutrition.

The hypodermis (fatty layer)

This is the fatty layer. It is the supportive layer of the skin and protects the body against cold. There are blood vessels and nerves in the dermis.


MACD002 The skin structure
Image: The skin structure




Melanocytes are cells that make a pigment called melanin. Melanin gives our skin, hair and eyes their colour. It also protects skin from the harmful effects of the sun.

When skin is exposed to sunlight, the melanocytes make more melanin. This is to absorb more of the harmful UV rays from the sun. This makes the skin look darker, or suntanned. A suntan is a sign that the skin is trying to protect itself.

If you have black or brown skin, you have the same number of melanocytes as people with white skin. But your melanocytes make more melanin. This means you have more natural protection from UV rays.

Moles are a group or cluster of melanocytes that are close together. They are sometimes called naevi.

About our information

  • References

    Below is a sample of the sources used in our melanoma information. If you would like more information about the sources we use, please contact us at

    Michielin O, van Akkooi ACJ, Ascierto PA, et al. Cutaneous melanoma: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up. Annals of Oncology. 2019; 30, 12, 1884-1901 [accessed May 2022].

    Michielin O, van Akkooi ACJ, Ascierto PA, et al. ESMO consensus conference recommendations on the management of locoregional melanoma: under the auspices of the ESMO Guidelines Committee. Annals of Oncology. 2020; 31, 11, 1449-1461 [accessed May 2022].

    Peach H, Board R, Cook M, et al. Current role of sentinel lymph node biopsy in the management of cutaneous melanoma: A UK consensus statement. Journal of Plastic, Reconstructive & Aesthetic Surgery. 2020; 73, 1, 36-42 [accessed May 2022].

  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Senior Medical Editor, Dr Samra Turajlic, Consultant Medical Oncologist.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

The language we use

We want everyone affected by cancer to feel our information is written for them.

We want our information to be as clear as possible. To do this, we try to:

  • use plain English
  • explain medical words
  • use short sentences
  • use illustrations to explain text
  • structure the information clearly
  • make sure important points are clear.

We use gender-inclusive language and talk to our readers as ‘you’ so that everyone feels included. Where clinically necessary we use the terms ‘men’ and ‘women’ or ‘male’ and ‘female’. For example, we do so when talking about parts of the body or mentioning statistics or research about who is affected.

You can read more about how we produce our information here.

Date reviewed

Reviewed: 01 October 2022
Next review: 01 October 2025
Trusted Information Creator - Patient Information Forum
Trusted Information Creator - Patient Information Forum

Our cancer information meets the PIF TICK quality mark.

This means it is easy to use, up-to-date and based on the latest evidence. Learn more about how we produce our information.