My 11 year old daughter got a bad sunburn yesterday. What helps prevent skin cancer in future?

Avoidance of the sun. The best prevention for skin cancer is sun avoidance. Uv light has cumulative effects on skin cancer risk (i.e. The more exposure the higher the risk.) long sleeve shirts, long pants, wide brim hats are best. Next would be a good quality sunscreen with a minimum SPF of 30 applied every one to two hours.
Prevent future burns. The burn will resolve with local treatment. In the future use sunscreen at least 15, and reapply every 4 hours if not in water. Skin cancer is related to sun exposure, fair skin color, and age. Avoid tanning beds in the future. Oral supplements with antioxidants amd well balanced multivitamins will help squelch free. Radicals. Add varied colored plant foods to diet.
Sunscreen. Using sun screen and limiting her exposure to uv radiation will decrease her risk. In addition having routine skin examination by a dermatologist will detect any abnormality at early stages.

Related Questions

What are the risks of skin cancer associated with albinism? What is the best way to prevent bad sunburns and keep my skin cancer risk low?

Yes there is a high. Use sun screens when you go out in sun...Avoid sun and wear protective clothing and plenty of sunscreens.
Sunscreen. Albinism is a major risk factor for developing skin cancers. It is important to use sunblock and to limit your exposure to uv radiation. Cover up with long sleeves and and a hat if you are going to be in the sun for prolonged periods of time. It is also important to visit your friendly dermatologist for complete skin examinations.

Does broad spectrum sunscreen help prevent skin cancer or does it just prevent sunburn and do nothing to prevent skin cancers?

UVB blockage. If the 'broad spectrum' sun screen blocks uvb, it will help in prevening skin cancer.
Sunscreen. Yes. We have good evidence that sunscreen prevents melanoma and other skin cancers.