1. background information on the skin
   
   
2. the effects of sunlight on the skin
   
   
3. the danger of skin cancer
   
   
4. references / further reading
   
   

Background information on the Skin.

In order to describe the effects that sunlight has on skin, it is important to look at some background information on the structure of the skin.

The skin is the largest organ in the human body. It has two main layers - the dermis and the epidermis. Below these two layers, there is a layer of fat called the subcutaneous layer.

The epidermis is the outer layer of skin. It is composed of five layers, the basal layer, the prickle cell layer, the granular layer, the clear layer and the surface. lymphatic vessels in the dermis supply the epidermis with fluids and nutrients as there is no blood supply to the epidermis.

Dead skin cells are constantly being shed from the skin's surface, a process called desquamation. Cells in the basal layer are continually dividing to form new skin cells which move towards the surface, (pushed up by the dividing cells below).

The dermis is the layer of skin below the epidermis. Most of the functions of the skin occur in this layer, that is why it is commonly known as the true skin.

Nerves in the dermis detect temperature and pressure and send this information to the brain. Blood vessels supply the new cells in the basal layer with nutrients and also remove waste products as well as helping to maintain the body's temperature.

Sweat glands also appear in the dermis layer, as do hair follicles. Tiny muscles called erector pili pull the hair upright in order to trap a layer of air under them in response to cold, this helps insulate the body and gives the skin a goose bump appearance.

The effects of sunlight on the skin

Sunlight has two main effects on the skin, it changes skin colour, and it makes vitamin D.

The explanation for how sunlight produces vitamin D in the skin is this: in the epidermis, there is a chemical called 7-dehydrocholecalciferol which turns into a pre Vitamin D substance after exposure to ultraviolet radiation. This pre-vitamin D then turns into real vitamin D under body heat and the action of enzymes in the kidneys.

According to Raymond Bonnett (sun and the skin - see references), walking around on a summer's day for 30-60 minutes would be sufficient to prevent a deficiency of vitamin D.

Vitamin D is essential for the metabolic control of the body's calcium balance, and as such is vitally important to development of bones and to maintaining their healthy state.

A vitamin D deficiency in children can cause a condition called rickets, which causes bones to grow abnormally due to a softening and 'bowing' of the bones. This condition can also occur in adults and is highly prevalent in old people who might have mobility difficulties and therefore can't get enough sunlight. In some cases, bones can become so fragile that they can break, which can sometimes lead to further complications.

Another source of vitamin D is dairy products such as milk, yogurt, cheese, butter and eggs. Including these dairy as part a diet can help to compensate for lack of sunlight.

When the body detects the presences of sunshine, it produces a hormone called MSH (melanocyte-stimulating hormone). This hormone causes melanocyte cells that occur in the basal layer of the epidermis to produce melanin. Melanin is the substance which produces the darkening (or tanning) of the skin. It is thought that process helps to protect the boy from the harmful effects of the sun's rays since dark colours absorb radiation.

Skin Cancer

Excessive exposure to sunlight can cause skin cancer, there are three types of skin cancer; Basal Carcinoma, Squamous Cell Carcinoma, and Malignant Melanoma.

Most skin cancer is caused by UV rays from the sun which damages the genetic information of the skin cell.

Basal cell carcinoma is a cancer that develops in the basal cells of the skin. Although it is the most common cause of skin cancer, cancer deaths from this particular cancer are rarely seen. This type of cancer normally invades local tissue over a number of years, rarely spreading to other organs or other parts of the body; however, it can have very damaging effects at a local level if it is not dealt with in time.

Squamous cell carcinoma is slightly less common than basal cell carcinoma; however, it can spread and become potentially lethal if it is not dealt with. This type of cancer manifests as a hard, scaly patch of skin with a central ulcer that has a red raised border.

Both of these types of cancer are 95% curable if caught early.

Malignant Melanoma is a cancer of the melanocyte cells. These are the cells that produce melanin, which causes darkening of the skin. Melanoma is the rarest form of skin cancer, but is the cause of most deaths from skin cancer. Unlike other types of skin cancer, melanoma spreads quickly to other parts of the body, making it highly dangerous.

Both skin cancer and rickets can be prevented through awareness of the risks involved and making sure that you get enough sunlight (especially in northern climates), and by being equally aware that you're not getting too much sunlight, more so in hot countries where the sunlight is much more intense.

Bibliography / References :

• Sun and the Skin
  Raymond Bonnett ISBN:1853172758
  
  
• An introductory Guide to Anatomy & Physiology
  Louise Tucker - ISBN: 1903348048
  
  
• 100 Questions and Answers about Melanoma and Other Skin Cancers
  Edward F McClay and Jodie Smith - ISBN: 0763720364
  
  
• SKIN BIOLOGY AND STRUCTURE: http://www.mydr.com.au/default.asp?Article=3718