Chemistry behind sunscreen’s action
Sunscreen is designed to protect us from UV radiation from the sun; this has a shorter wavelength than visible light and a lot of the energy emitted by the sun is in the form of UV, which can be divided into three categories. One of these, UVC (with a wavelength of ~290-100 nm) isn’t a problem, as it’s absorbed by ozone in the atmosphere before it can reach the Earth’s surface. There are two other categories, however, UVA & UVB, which can cause damage to skin.
UVB (wavelength ~290-320 nm) is responsible for around 5% of the UV radiation reaching Earth, with the majority of it also being absorbed by the atmosphere. It causes your skin to produce more melanin, which is what causes the tanning effect of sitting in the sun. However, it can also cause sunburn and direct DNA damage, which can increase the risk of developing skin cancer. Sunscreen has been available as a product since around 1928 and most early sunscreens were formulated to screen the skin against UVB rays.
UVA (wavelength ~320-400nm) is responsible for the largest proportion of the UV radiation from the sun that reaches the Earth’s surface – approximately 95%. UVA can penetrate much deeper into the skin than UVB, down into the connective tissue. This causes wrinkling and premature ageing of the skin. UVA can also generate reactive species in the skin, and thus indirectly causing DNA damage and contribute to an increased skin cancer risk. It was for a time considered relatively harmless in comparison to UVB, but now the damage it can cause is beginning to be understood, sunscreens have included different chemicals to also shield against this portion of the UV spectrum.
Sunscreen is basically a lotion that protects the skin from the ultraviolet radiation of sun. Sunscreen lowers the risk of skin cancer and reduces the skin damage. Many people consider that sunscreens are similar to that of sunblock. However, they are different types of sun protection. Most sun protection products work by absorbing, reflecting or scattering sunlight. However, sunscreens provide protection from the two types of damaging ultraviolet (UV) rays namely UVA and UVB. Both of these rays can cause sunburns and can lead to longer-term health effects such as skin cancers, premature skin aging and eye damage. Sunscreen is principally a chemical defence and it works by penetrating the skin followed by absorbing the UV rays before they reach and damage the dermal layers. Although many chemical compounds are there to absorb UV rays but oxybenzone, avobenzone, and para-aminobenzoic acid (PABA) are the common ingredients.
