While in the short term the sun has a positive effect on how we feel and how we look, over time the cumulative effect of frequent exposure to the sun’s rays can cause severe damage to the skin. It is exposure to the sun that is primarily responsible for our wrinkles and so-called age spots. The process is called photoaging. Not only does the sun accelerate our rate of ageing, it can also increase our chances of developing skin cancer.
There are three layers of skin: the epidermis which is the outer layer; the dermis or middle layer; and the subcutis or bottom layer. The dermis contains elastin and collagen which are responsible for the skin’s structure and its youthful appearance. It is this layer that is damaged by UVA radiation from the sun while it is UVB radiation that is mainly responsible for sunburn. UVA damages the collagen fibres and this causes then to produce abnormal elastin which in turn triggers production of metalloproteinases enzymes which have the role of rebuilding damaged collagen, however this process is imperfect and result in imperfectly rebuilt skin. Thus over time wrinkles appear and the skin takes on a leathery appearance.
While photoaging is best combated by keeping out of the sun, but we all need a certain amount of exposure to sunlight; the skin makes vitamin D, which is necessary to keep us healthy, using sunlight. However avoiding the sun when it is at its most intense, wearing a wide brimmed hat, and using sunscreen all help reduce photoaging. The effects can also be attenuated by the use of topic applications of creams that contain retionoids (vitamin A) and antioxidants.
UVB rays only penetrate the epidermis, but they are responsible for causing damage to the DNA of cells that make up this layer. UVA penetrates the skin more deeply than UVB and it is responsible for photoaging, however it also damages DNA of the cells in the epidermis adding to the effect of the UVB. It is in the epidermis where most skin cancers occur.
The cells that are damaged are the keratinocytes in the basal epidermis, and the damage is cumulative, leading initially to red scaly spots called actinic keratoses which can develop into malignant skin cancer.
Antioxidants and topical retinoids such as vitamin A creams along with anti-oxidants are an effective way of preventing and slowing down the process.