If you’re very sensitive to the sun, wear sun-protective clothing in addition to sunscreen.
Clothes vary in their ability to block ultraviolet (UV) rays. Tightly woven and darker fabrics, for example, block best. Some clothes are treated with a UV-blocking chemical.
You can also sun-proof your clothes yourself by using a UV-absorbing laundry additive called Sun Guard. According to the company, it gives clothes an SPF of 30, which lasts through 20 washings (an untreated tee shirt has an SPF of 5 to 10).
If you're interested in sun-protective clothing, the Skin Cancer Foundation offers a searchable list of companies that have its Seal of Recommendation.