The rays of the sun are most concentrated during summer which is why it is hottest during the summer. UV rays from the sun stimulate the pituitary gland which in turn produces (melanocyte-stimulating hormone). This hormone travels through the bloodstream and reaches the melanocytes. Melanocytes are present in an equal amount in every person's skin. However the amount of skin pigment (melanin) that they produce differs. When you go out in the sun, a certain amount of sunlight (and therefore radiation) is reflected away from your skin surface while some of it gets absorbed by the skin. UV rays damage your DNA structure and prolonged exposure to sunlight will increase your risk of skin cancer.
Skin tanning is a two step process in which there is "immediate pigment darkening" and "delayed tanning". When your skin is exposed to UV rays, melanin production increases immediately. This causes your skin to darken within a few minutes and although it is not easily noticeable in fairer skinned people, it is very obvious with darker skinned people. It is triggered by ultraviolet type B radiation. On the other hand, delayed tanning is slower and takes more time to develop but its effects last longer. It is actually caused not by the UV rays themselves but by the damage they have caused to an individual's DNA. It is triggered by UVA radiation.
Whenever you go out into the sun, make sure that you use a sunscreen lotion. All sunscreen lotions have a label that denotes their sun protection factor (SPF). If the number is higher it means that the sunscreen offer greater protection. Ideally a sunscreen with an SPF of 30 would absorb about 96.7 percent of UVB radiation. It is important that you buy a sunscreen lotion that contains both UVA and UVB filters.
answered by G M