How does sunscreen work?

Sunscreen is made up of a mixture of organic and inorganic particles to protect your body from potentially harmful UV radiation. The sunlight is made up of various different types of UV radiation; these include UVA, UVB and UVC radiation. Each of these types of UV radiation is of different wavelength which makes the sunscreen easier or harder to protect your skin from burning. For example UVC radiation has a wavelength of 280 -100mm, this very short wavelength radiation are blocked by the earth’s atmosphere even before it reaches you. But not all sunscreens protect against UVA radiation and over exposure to this type of radiation can, over time cause skin cancer.

The organic particles within the sunscreen (often a chemical called octyl methoxycinnamate or oxybenzone) absorb the rays; these are then dissipated within the body as heat which therefore prevents your skin burning. The inorganic particles (often zinc oxide or titanium dioxide) reflect and scatter the radiation which forms a physical barrier and therefore also helps prevent the skin from burning. It is these inorganic particles in the sunscreen which makes it appear white; however nowadays the particles are so small the sunscreen is clear so you can’t see it.

Clearly labelled on every sunscreen bottle is the “SPF” which stands for the sun protection factor. This only measures the amount of UVB radiation protection which that particular sunscreen provides. This SPF works on the basis that you would burn if you were in direct sunlight for one hour and therefore with an SPF 15 you could stay in the sun for fifteen hours. However this should only be treated as a basis given that there is a higher level of UV radiation at midday since the sun is lower in the sky. So the amount of time that you can spend safely out in the sun depends on the time of day as well as the level of sunscreen that you have applied and how well the sunscreen has been absorbed.