This is one of those rare times when we tell you store-bought is better than homemade!

Here at TreeHugger we are big fans of natural skin care and cosmetics, but not at the cost of bad sunburns. When it comes to sunscreen, it’s best to steer clear of homemade concoctions, no matter what Pinterest tells you. The female-geared aspirational-lifestyle website is full of recipes for homemade sunscreen, but, according to a new study just published in Health Communication journal, these are little more than a recipe for sunburn and skin damage.

Researchers analyzed 189 pins selected randomly from Pinterest and found that 95 percent of these “positively portrayed the effectiveness of homemade sunscreens,” while 68 percent recommended recipes with insufficient SPF protection. A mere 35 percent contained zinc oxide in their ingredient lists, and many claimed to get their SPF value from ingredients such as coconut, raspberry, carrot, olive, and lavender oils, shea butter, and beeswax, all of which provide less than 15 SPF.

Homemade sunscreens do not work for several reasons, according to a detailed article from the School of Natural Skincare. First, carrier oils do not have sufficient SPF levels to provide adequate sun protection, and claims that they do are because scientific studies have been misinterpreted.

There are two ways to measure UV absorbance. One is ‘in vitro’, which measures the amount of UV light a certain material (carrier oils, in this case) absorbs. The other is ‘in vivo,’ which measures “the reaction of the skin to the UV light (redness or erythema) and at what dosage of UV light it appears on skin treated with sunscreen vs untreated skin.” The latter, in vivo, is the best test of sun protection.

“With carrier oils it is difficult to extrapolate absorbance measurements to SPF levels because we do not know what happens when the oil is exposed to sunlight, air, and hot summer temperatures. It might start to oxidize and release free radicals that harm the skin. So, until actual in vivo measurement are done, there is no way of knowing how much protection from the sun carrier oils offer.”

Second, zinc oxide doesn’t automatically provide sun protection. When mixed, it clumps together microscopically, which means it can look smooth and blended, but in reality leaves space on your skin to burn.

“This is why professional equipment is absolutely necessary – this means a high shear mixer/homogenizer; the price for this piece of equipment starts at $600. Regular kitchen stick blender simply won’t do the job. Also, special ingredients that work as dispersing agents, for example polyhydroxy stearic acid, are also vital for a mineral sunscreen.”

Third, SPF levels need to be tested in order to know what you’re putting on your skin. These usually take the form of in vitro tests and a final SPF determination test, conducted on volunteers. Unless you have these numbers, it’s impossible to know how protected you truly are and you’ll end up “playing Russian roulette with your skin.”

The best and safest choice is to buy FDA-tested (and EWG-approved) sunscreens with a physical sunblocking ingredient, such as titanium dioxide or zinc oxide. There are plenty of great products on the market today that can do the job well. By all means, spend time perfecting other DIY skin care recipes, but spare yourself the possible skin damage and leave the sunscreen-making to the professionals.