Jessica Alba's "Honest" company has been criticized for being frauds but it's not alone. Though the variation in cost for sunscreen protection averages well over 3,000, the variation is protection is not very much.

Like with organic food, you don't get what you pay for - unless what you are paying for is self-identification. But no matter what you pay or why you buy, you may not be getting a product that meets the American Academy of Dermatology's guidelines for sunscreens. This was largely due to a lack of water or sweat resistance, according to a new Northwestern Medicine study.

Though skin cancer is rather common, sunscreen use is low for adolescents and adults. And, if they do wear sunscreen, they don't use enough or apply it frequently enough. Cost and "cosmetic elegance" of the product -- how it feels on the skin, color or scent -- may be factors. Or it could be the naturalistic fallacy that has ballooned into a $100 billion industry, namely that if it's found in nature it can't be harmful.

Northwestern Medicine investigators wanted to identify high performing products that are affordable and popular to know what to recommend to their patients and, hopefully, increase the likelihood of their using it. They ended up being surprised at the large variation in price, with no discernible difference in the products. To identify the most popular sunscreens, investigators looked at the top rated 1 percent of the 6,500 sunscreens with four or more stars sold on Amazon.com. They came up with the 65 top-rated products. The goal was to identify high performing products that are affordable and popular to encourage adherence to sunscreen use. 

Their median price was $3.32 an ounce; median SPF was 35; 92 percent had broad-spectrum coverage claims and 62 percent were labeled as water or sweat resistant. The cheapest sunscreen was 68 cents an ounce and the most expensive was $24 an ounce.

If they are not water or sweat resistant, they may not be much good.

"Dermatologists should have a voice in consumer choices when it comes to skin health, a voice that takes the patients' best interests at heart and is not influenced by marketing claims," says
said Dr. Steve Xu, a resident in dermatology at Northwestern University Feinberg School of Medicine and lead author of the paper in JAMA Dermatology.

So don't buy something because Gwyneth Paltrow says it will make you a better parent.