It is often said that Cape Town will have four seasons in a day. What is interesting, is that a patient may be exposed to certain types of UV-rays more on a cloudy day than on a sunny day. Sunlight is composed of different types of ultraviolet rays. For our purposes mainly UVB and UVA. The one that commonly makes you feel like you are burning in the sun is UVB.
UVA is responsible for photo-ageing and certain types of skin cancers. The clouds are able to absorb most of the UVB, but do little to absorb the UVA. On a cloudy day, you therefore feel less burn, but are still exposed to excess amounts of UVA.
This is because your body is not prompted to seek shade or you are less likely to wear sun protective clothing or sunscreens when you don’t feel the burn. Therefore be sun safe weather depending!