Effects of UVR on skin

Over exposure to UVR can cause sunburn (erythema), skin damage, premature aging, and skin cancer. 

Sunburn is the most common effect of UVR on skin.  It results in bright pink or even red skin, swelling, blistering, and pain.  If the sunburn is severe or extensive it can result in nausea, fever or chills, and tachycardia, and dehydration.  The pain that we experience is a result of the body’s reaction to the UVR skin damage, whereby an increase in several chemical substances including prostaglandins and histamines is triggered.  These chemicals contribute to inflammation.  In cases of extensive sunburn there can be increased levels of serum interleukin-1 and interleukin-6 as well.

Skin damage and premature aging are long term effects of exposure to UVR even in the absence of sunburn.  Sun exposure causes the outer layers of the skin to thicken and long term exposure can cause skin to wrinkle, sag and become leathery.  Coarse wrinkling and elastosis which gives the skin a pebbly, yellowed quality are also common effects.  Both wrinkling and elastosis are caused by damage to elastic fibres in the dermis.  UVR exposure can also result in irregular hyperpigmentaion and depigmentation.

A person’s cumulative exposure to UVR along with the number of severe sunburns and their skin type, increases their risk of developing skin cancer.  Skin cancers affect people of all skin types.

Malignant changes in the skin usually occur in the epidermis, the surface layer of the skin.  However, the degenerative changes occur first in the under layer, and are not obvious in the outer layer until much later.  In other words, there tends to be a conditioning effect on the structures of the skin over a period of time before skin cancers are produced.

One of the earliest changes in the skin as a result of UVR is in the formation of solar keratoses.  A solar keratosis is an overgrowth of the epidermis to form a scaly layer on the skin.  Solar keratoses will sometimes clear up if exposure is stopped before they become too established.  They are potentially malignant and can develop into cancer.  They do not show a spreading or surface growth like other keratoses, but they can become early forms of a squamous cell carcinoma (SCC), a type of skin cancer that can spread to other parts of the body.  The body’s immune system has a mechanism for clearing up these early spots, but this effort can be inhibited by UV light which damages the key cells involved (including the Langerhans cells of the epidermis).

Research suggests that whereas UVB plays an important role in skin cancer initiation, oxygen radicals formed in response to UVA or inflammation appears to be critical in causing progression of the pre-malignant lesion into a fully developed tumour.

A basal cell carcinoma (BCC) is a malignant tumour that rarely spreads to distant sites.  It starts in the basal layer of cells, and grows upwards from there.  It consists of immature cells and has an organized complex of supportive tissue around it.  BCCs are the most common malignant skin tumours in humans and are most common in areas of skin most exposed to UVR.

A squamous cell carcinoma (SCC) arises from the cells above the basal layer of the epidermis and usually appears after many years of exposure to UVR.  The cells at this level have started to mature towards keratin formation and the cancer occurs when they accelerate in growth and break through the basement membrane into the dermis.  In its early stages a SCC will appear as a thickening that feels firm with ill-defined limits.

A melanoma is malignant and arises from skin cells called melanocytes (melanin producers).  Although it is thought that UVR causes melanomas they often appear on parts of the body that have had little or no sun, and a recent study found that UV products do not lessen the chance of a melanoma forming.  It is possible that there is a factor produced by UVR on the skin which circulates, and stimulates the melanocytes.  Once the growth of a melanoma is triggered it continues to spread either radially or vertically or both.