Ultraviolet (UV) radiation is emitted by the Sun and penetrates the Earth’s atmosphere. Ultraviolet A (UVA) and Ultraviolet B (UVB) refer to different wavelengths.

Some exposure to UV radiation is beneficial, because it enables our skin to produce essential vitamin D. This is important for the function of bones, blood cells and our immune system.

But too much UVA and UVB can cause skin damage and premature ageing, and lead to skin cancer. It can also damage eyes.

Levels of UV radiation vary throughout the day.

The highest readings occur in the four-hour period when the sun is at its highest – usually from late morning to early afternoon.

The UV Index is a standard measure of UV radiation used around the world.

Values start at zero and can rise above 10.

According to Cancer Research, if the UV index is three or above, you should consider using sunscreen and covering up. Higher readings require more protection.