Dermatologist used a scale called Fitzpatrick scale or Fitzpatrick skin type (FST) to classify the various types of skin tone based on the response of the skin to ultra-violet radiation (UVR). According to this scale there are 6 skin types.
What determines your skin type?
The skin is composed of several layers of cells. The melanocytes, which are cells present in the epidermis (the superficial layer of the skin), are responsible for the variation in the skin colour of human race. Note that it is not the number of melanocytes but the size of the melanosomes and the type of pigment produced by these cells (also called the activity of the melanocytes) that determine the skin colour of an individual.
One melanocyte is associated with 30-40 (1:36) surrounding keratinocytes, which are the fundamental cells of skins. The keratinocytes engulf the melanosome containing melanin (pigment responsible for skin color) which results in the skin pigmentation.
Effect of the sun on skin pigmentation
A single exposure to UVR increases the size of the melanocyte with increase in the activity of the enzyme required for melanin synthesis (tyrosinase). Repeated UVR exposure leads to increase in the number of highly active melanosomes as well as increase transfer of melanosomes to the neighbouring keratinocyte which results in tanning (see the little brown dots in the above diagram).
What is the role of tanning?
You can think of tanning as a way the skins naturally defends itself against the oxidative stress produced by the sun exposure. Tanning is physiological protective response to UVR. Melanin acts as a natural antioxidant which quenches the harmful oxidative radicals produced by the chemical reaction which takes place on UV exposure.
Melanin provides a natural sun protection factor (SPF) of 13.4 in black individuals and only 3.4 in pale skin individuals.
Individuals with FST I, II who do not tan with sun exposure are at higher risk of developing skin cancers.
Influence of fashion
The fashion trend influences pale skin individual to desire a darker skin tone which leads them to go through extensive lengths to obtain that “perfect tan” either by prolonged sunbathing at the beach or by artificial tanning machines without considering the risk they impose on their health in the name of “beauty”.
On the other hand darker skin individuals with relatively lesser risk of cutaneous cancers from UVR ironically hide from the sun as society has made them believe that fairer skin is synonymous with beauty.
Why do you need to know your skin type?
Knowing your skin type helps you understand the risk of developing skin cancers with UV exposure. Individuals with FST I, II need to strictly adhere to proper sun protection in the form of broad spectrum high SPF sunscreen and protective clothing especially if they are living in tropical countries.
Disorders of pigmentation like melasma, or pigmentation that can occur from either disorders such as acne, or as a complication of procedures such as LASERS, or chemical peels, etc. are more common in individuals with darker skin tone (FST III,IV,V VI). Therefore caution must be taken while carrying out procedures in such individuals.
Consumers must also understand that some studies on the efficacy of certain active ingredients for a particular disorder are performed solely in individuals of lighter skin tone and the same results may not reflect in their skin type. Therefore referring to studies done on individuals of same ethnicity holds more value. For example you should search for studies done on Indian population if you are Indian.