SPF stands for Sun Protection Factor, a measure of how long your sunscreen will protect your skin from the sun. Therefore, when using a sunscreen with SPF 50, your skin does not burn until it has been exposed to 50 times the amount of sun energy that would normally cause it to be burned. The amount of sun energy your skin is exposed to depends not only on the amount of time it is exposed to the sun, but also on the time of day at which the exposure is made.
Ultraviolet rays: UV rays are an invisible form of radiation. They can penetrate the skin and damage cells. Sunburn occurs when the amount of exposure to the sun or another source of ultraviolet rays exceeds the ability of the body’s protective pigment, melanin, to protect the skin. Only 5% of the sun’s radiation that reaches the earth is UV radiation, and there are several types: while UVC radiation is blocked by the ozone layer, UVA and UVB radiation reach the earth and affect the skin.
UVA rays: UVA radiation makes up 95% of the ultraviolet radiation that reaches the skin’s surface. It passes through clouds, glass and the epidermis; unlike UVB radiation, it is painless and can penetrate very deep into the skin to reach the cells of the dermis. Because they produce free radicals, they can alter cells in the long term and cause
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- Photo-aging: A change in the orientation of elastin and collagen fibres that causes the skin to sag and lose its firmness, and wrinkles to appear
- Sun intolerance, commonly known as solar allergies (redness, itching, sunburst)
- Pigmentation diseases (mask of pregnancy, spots)
- Skin cancers.
UVB rays: UVB radiation constitutes 5% of the ultraviolet radiation that reaches the earth. It is responsible for tanning, but also for burns (sunburn), allergic reactions and skin cancers.