Why does my skin hurts & burns in the sun when overcast?

Sun sensitivity: Certain medications, chemicals and medical conditions can make the skin more sensitive to the sun (photosensitivity). For example, an ingredient in your shampoo or having a condition such as lupus can increase photosensitivity. In most cases this isn't a true allergic reaction. However, it can cause symptoms similar to those caused by a sun allergy — and if you already have a sun allergy, it can m.