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Sun Care and the effects of UV radiation

Types of UV radiation

When we talk about protecting our skin against the sun, we are talking about protecting ourselves from its Ultraviolet (UV) radiation. The sun gives off UV radiation that we divide into 3 categories based on the wavelength:

I. UVC radiation is almost completely absorbed by the ozone layer and does not affect the skin.

II. UVB affects the outer layer of skin, the epidermis, and is the primary agent responsible for sunburns.

III. UVA was once thought to have a minor effect on skin damage, but now studies are showing that UVA is a major contributor to skin damage. UVA penetrates deeper into the skin and works more efficiently.

UV skin damage caused by excessive sun exposure

It isn't possible or practical to completely avoid sunlight, and it would be unwise to reduce your level of activity to avoid the outdoors. Small periods of time in sunlight also help your body make vitamin D, which can be important for good health. However, too much sunlight can be harmful.

Some of the possible mechanisms for UV skin damage are collagen breakdown, the formation of free radicals, interfering with DNA repair, and inhibiting the immune system.

In the dermis, UV radiation causes collagen to break down at a higher rate than with just chronologic aging. Sunlight damages collagen fibres and causes the accumulation of abnormal elastin. When this sun-induced elastin accumulates, enzymes called metalloproteinases are produced in large quantities.

Normally, metalloproteinases remodel sun-injured skin by manufacturing and reforming collagen. However, this process does not always work well and some of the metalloproteinases actually break down collagen.

This results in the formation of disorganized collagen fibres known as solar scars. When the skin repeats this imperfect rebuilding process over and over, wrinkles develop, resulting in pre-mature skin aging.

Free Radicals

UV radiation is one of the major creators of free radicals. They can damage cell function and alter genetic material. Free radical damage causes wrinkles by activating the metalloproteinases that break down collagen. They change the genetic material, RNA and DNA of the cell, resulting in higher incidences of pre-cancerous lesions, melanoma and non-melanoma skin cancers.

Other changes to the skin

1. Skin Colour changes

Skin colour changes caused by sun exposure are common. The most noticeable sun-induced pigment change is brown spots called solar lentigenes. Light-skinned people are particularly prone to freckles.

2. Freckles

Large freckles, also known as age or liver spots, can be seen on the backs of the hands, chest, shoulders, arms and upper back.

3. Moles

Moles (nevi) are usually seen in sun-exposed areas. Although it is normal to acquire new moles from childhood through young adulthood, their formation is stimulated by the sun.

4. Skin lesions and cancer

Pre-cancerous skin lesions related to excessive sun exposure are called solar keratoses if they appear on the skin and solar cheilitis if they appear on the lips. They are considered premalignant lesions because 1 in 100 cases per year will develop into squamous cell carcinoma, another type of skin cancer.