It is well-known that people tan at different rates depending on their skin properties. There are several classifications of skin types made to predict sensitivity to sunlight and risk of skin cancer based on various skin properties.
Protective Mechanisms Of The Skin
The superficial layer of the skin is called the stratum corneum, and it is composed of dead skin cells called keratinocytes. This layer represents the first barrier for UV radiation. The second barrier is melanin, a dark pigment that gives the skin its color. Scientists state that skin pigmentation is a far more important protective factor than the stratum corneum. Black-skinned people have more melanin in their skin, and their melanin is dispersed in such a way to optimize the protection, while white-skinned people's melanin-containing organelles are grouped to provide less efficient protection. With that in mind, black people are better protected from the destructive effect of UV radiation than white people.
Measuring Your Sensitivity To Sunlight
Sensitivity to sunlight is determined by two parameters: the acute destructive effects on the skin - erythema (redness), and pigmentation (tanning) induced by sunlight. These are the effects of the ultraviolet (UV) spectrum of sunlight.
The most accurate test of sensitivity to sunlight is a phototest with a solar stimulator. The skin is exposed to increasing doses UV radiation for certain amount of time, and skin changes are observed 20-24 hours later. This test can be used to determine the minimal dose of UV radiation that can cause sunburns in a particular person.
In 1975, the dermatologist Thomas Fitzpatrick developed a scale for skin-type determination that uses a questionnaire to classify skin types. There are four possible skin types for persons with white skin (I, II, III, IV), and two for persons with brown skin (V and VI).
Type I, for example includes people with very white skin, red or blonde hair, blue eyes, and freckles, whose skin always burns and never tans, while type VI includes black persons who never burn and tan very easily. This scale is used by dermatologists to determine which level of skin protection is needed during sunbathing to prevent burns very often.
Skin Type And Cancer Risk
Fitzpatrick's scale is also used to determine the risk of skin cancer, as it is well-known that various types of skin cancer are induced by UV radiation, such as basal cell carcinoma and cutaneous malignant melanoma. Albinos (people with a congenital lack of melanin) have a higher risk of skin cancer than other people. This proves that pigmented skin is more resistant to chronic destruction than non-pigmented skin.
In conclusion, skin-type determines your ability to tan, as well as your risk of sunburns and skin cancer. If you fall under type I or II of the Fitzpatrick's scale, it is highly recommended that you avoid high doses of UV radiation and to use products with a high sun protection factor (SPF).
Choose the appropriate product according to your skin type. For example, if you usually get sunburns after 15 minutes of exposure, you will get them in 300 minutes with a 20-SPF product (15*20=300). Do not buy products with ridiculously high SPF, as studies suggest that SPF above 50 does not increase the protective effect.
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