Sun damage may not be visible at an early age, but multiple studies warn of the consequences later in life. Sun exposure damages fibres in the skin called elastin, resulting in skin laxity. UV rays alter the DNA, causing saggy skin, lines, wrinkles, discolouration, age spots, and even cancer.
UV radiation is composed of two different wavelengths, UVA and UVB. When the skin is exposed to UV rays, melanin is photo-oxidised (immediate pigment darkening). This is the process that darkens your skin as it attempts to block out the radiation. Prolonged or repeated exposure to UV radiation results in persistent pigment darkening and eventually long term tanning (delayed tanning) which increases both the amount and activity of melanocytes. The delayed tanning process can last 10 days to several weeks, and with repeated exposure can cause DNA photo-damage.
UVB rays cause sunburn, but it is the UVA rays, with their longer wavelength that penetrate deep into the dermis, that are responsible for photo-ageing of skin. Sensitivity to sunburn is routinely evaluated by minimal erythema dose (MED). MED describes the lowest dose (J/cm2) of UV radiation that will cause erythema assessed 24 hours after exposure. Higher MED means higher tanning capacity. Darker skin is a result of increased number of melanin: it acts a barrier to the UV radiation.