Sunscreens come in many different strengths but dermatologists recommend using one that has a Sun Protection Factor of 30 or more to help prevent skin cancer. Your sunscreen should also offer “broad-spectrum” protection against UVA and UVB rays. Look for water-resistant brands. Reapply every two hours whether it’s sunny or cloudy. Sunscreens expire over time and exposure to heat, so check the date on the bottle.