Too much sun can turn your hair into a brittle, dry mop that breaks and splits easily. This is especially true in those with blonde or grey hair. And if you already have thinning hair, you risk a sunburn on your scalp. Choosing hair care products with sunscreen provides some protection, although it can be hard to coat your hair evenly. That's why it's a good idea to wear a hat when you're out in the sun -- especially if your scalp is exposed. Choose a hat made of sun-protective fabric with UPF 30 (ultraviolet protection factor).