The Fitzpatrick scale is a system for classifying human skin tone and its response to exposure to UV light. On one end of the scale, Type I skin always burns when exposed to sun, and never tans. Meanwhile, Type IV never burns in the sun.
Here are the 6 types according to the Fitzpatrick scale:
Type I: (Always burns, never tans) Very pale, and commonly has freckles.
Type II: (Usually burns, and only occasionally tans)
Type III: (Mild burns, tans in a uniform manner)
Type IV: (Occasionally burns, usually tans) Moderate dark/brown skin
Type V: (Very rarely burns, and tans quite easily) Dark skin
Type VI: Never burns, very dark skin