Pigmentation

Sun Damage

How the Sun Damages our skin

The sun emits a broad spectrum of light, heat and other radiation, whilst the great amount of the Suns energy is absorbed by the Earths atmosphere, depending on the time of year (season), atmospheric conditions and where we live; varying amounts of light, heat and other radiation reach the earths surface.  Of the radiation that reaches that we will be exposed to, Ultra Violet is the most relevant as regards potential damage to our skin.

Excessive exposure to UV damages the skin permanently and may cause skin cancer, including malignant melanoma, one of the most lethal of cancers.

The three classes or wavelengths of Ultraviolet (UV) radiation are UVA, UVB and UVC. The earth’s atmosphere absorbs nearly all of the UVC, which is the most hazardous.  UVA and UVB radiation are both factors in sunburn, but our skin reacts differently to each one:

• UVA penetrates into the deep layers of the skin and causes damage where new skin cells are created.
• Wrinkles, age spots and sagging skin also result from long term exposure to UVA radiation.
• UVB affects the surface skin layer. The skin responds by releasing chemicals that dilate blood vessels causing inflammation and sunburn.

Skin explained

To better understand how the Sun damages our skin we need to have some basic understanding of our skin and its structure.

Skin is the largest organ of the human body.  It is flexible, to allow movement, but still tough enough to resist breaking or tearing and varies in texture and thickness depending on the part of the body. For example: the skin on our lips and eyelids is very thin and delicate, while skin on the soles of the feet is thicker and harder. Our skin is a good indicator of our general health.  If we are sick, it often shows in our skin.

• Some of the different functions of skin include:
• A cooling system via sweat;
• A first line of defence against bacteria and other organisms; and
• A sense organ that gives us information about pain, pleasure, temperature and pressure.

Humans lack a complete cover of body hair and consequently human skin has evolved as significantly different from the skin of any other warm blooded mammal. 

Layers of the Skin – epidermis

The visible (outer) layer of skin is the epidermis. The epidermis protects the more delicate inner skin layers, and comprises several ‘sheets’ or layers of cells. The bottom layer is where new epidermal cells are created.  As old, dead skin cells are shed from the surface, new skin cells are pushed up to replace them.  The epidermis also contains melanin, the pigment that gives our skin its colour.

Layers of the Skin – dermis

The dermis is the next skin layer below the epidermis; it is made of elastic fibres (elastin) for suppleness and protein fibres (collagen) for strength.  The dermis contains sweat glands, sebaceous glands, hair follicles, blood vessels and nerves.

Nerves

Both the dermis and epidermis have nerve endings. These transmit information on temperature, sensation (pleasure or pain) and pressure. Some areas such as the fingertips, lips and sexual organs have more nerve endings than other parts of the body.

Glands and blood vessels

The dermis is richly endowed with blood vessels.  In hot weather or after exercise, these blood vessels expand (dilate), releasing body heat to the skin surface.  Perspiration weeps out of sweat glands and evaporates from the skin, cooling us. 

 
If the temperature is cold, the blood vessels in the dermis contract, helping to reduce heat loss.

Sebaceous glands in the dermis secrete an oily substance called sebum that lubricates our skin.