lupus and cloudy days

I know that we must cover up from the sun light when you have lupus, but do we need to still cover up for cloudy days?

Clouds block UV by differing amounts, depending on the type of clouds and their height, thickness, and density.

Really thick, dense, dark, thunderstorm-type of clouds block UV fairly well, but many other clouds only block a little.

So, yes, as GreenBeans says, you should still cover up on cloudy days. Clouds aren't reliable in blocking UV.