How does a suntan protect against sunlight

Melanin is a complicated mixture of optically absorbing materials. chromophores), of which melanin is the most important. Melanin is a complicated mixture of optically absorbing materials, formed as an end product during the photo-assisted metabolism of the amino acid tyrosine. Both are bound covalently to the surrounding proteins within the skin, and other pigmented regions of the body. 

Melanin from natural sources falls into two general classes. The first component is pheomelanin (I), which has a yellow-to-reddish brown colour, and is found in red feathers and red hair. The other component is eumelanin (which has two principal components, II and III). Eumelanin is a dark brown-black compound, and is found in skin, hair, eyes, and some internal membranes, and in the feathers of birds and scales of fish. Melanin is particularly conspicuous in the black dermal melanocytes (pigment cells) of dark-skinned peoples and in dark hair and is conspicuous in the freckles, and moles of people with lighter skins. 

Melanin is formed by a photochemical reaction, so the concentration of melanin within the human epidermis (the outer layer of the skin) increases following exposure to photochemical reactions with tyrosine in the skin. This increase is seen readily by the formation of a suntan. This increase in the concentration of melanin following exposure to the sun is more obvious for fair-skinned people, although darker people usually tan more quickly because melanin is produced more efficiently in their skins. 

Unfortunately, melanin does not protect against all UV light, only that of wavelengths longer than 370 nm. We can readily show this 

A suntan is merely an increase in the concentration of melanin in the skin. 

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