• UV rays make up just 5% of solar radiation reaching the earth, but they are very powerful. There are various different types, and each kind of UV has different effects on skin.

• UVA make up 90% of UV rays reaching the earth. They pass through clouds, glass and the epidermis, allowing them to reach the dermis.
Their effects on skin are not felt, as they are not painful.
They are responsible for skin aging, allergic reactions and skin cancers.

• UVB make up 10% of UV rays reaching the earth. They are highly energetic and blocked by clouds or glass, although they can enter the epidermis.
They are responsible for tanning, but also sunburn, allergic reactions and skin cancers.

• UVC have a short wavelength and are entirely filtered out by the ozone layer. They do not reach the earth's surface.

• The epidermis : is the skin's superficial layer. Its surface is covered with dead keratinized cells that rub off. It forms a barrier that protects us against environmental stresses.

• The dermis : , situated beneath the epidermis, is a type of connective tissue. Its thickness varies depending on its location on the body.

• The hypodermis : is the deepest and thickest skin layer.

• Heat : one of the benefits associated with sun is the heat it provides. This heat is transmitted via the energy carried in the infra-red radiation of sunlight.

• Mood : sun has an effect on our mood and can be an excellent treatment for certain types of seasonal affective disorder, generally found in women during periods of limited daylight.
Affected individuals experience fatigue, a loss of interest in daily life and an increased need for sleep..
All of these symptoms can disappear as soon as the sun returns.

• Vitamin D : UV light is necessary for the synthesis of vitamin D, which is essential for fixing calcium within the bones.
15 minutes exposure per day is enough to manufacture sufficient vitamin D in fair-skinned blonds or red-heads.
By contrast, people with a pigmented skin type require longer daily exposure.
Even an overcast sky provides enough UV to ensure vitamin D synthesis. Brief exposure (15 mins) twice a week is sufficient.