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You could try a supermarket or a skincare store. You could even look at stores online. This will give you access to a wide variety of sunscreens so that you can familiarize yourself with your options. If you aren't sure where to start, try looking at a general marketplace such as Amazon.com. They have many sunscreens and also list the ingredients so that you can learn about them. Don't just look at the way they advertise themselves, but take the time to read through each ingredient. Be on the lookout for any potentially harmful ingredients and for helpful ones. A sunblock isn't as good as its label; it's as good as its ingredients. Think about which ingredients you want ahead of time so that you won't get lost reading list after list of indecipherable chemicals. Perhaps you are looking for something with zinc oxide and no oxybenzone. Focus your search on these criteria to find the best sunblock for you. If you find one that you like but you aren't ready to buy it, write down its name so that you can read up on it later. This can help you to make an even more informed decision. After narrowing down your search, find which one most closely aligns with your needs. There will likely be at least a couple of options that meet your criteria. Take the time to look at these more closely and factor in other requirements that you might have. Which one is water-resistant? Which one is broad spectrum? Which one has fewer chemicals? Which one costs less? Look at any aspects that are important to you and there will likely be one that stands out. If there are a few that seem about equal, go ahead and just pick one and give it a try. If you have enough money, consider buying two so that you can try them both and see which you prefer. Whatever you do, make sure to educate yourself before you choose a sunscreen. This is an important decision that can help protect you from cancer! Don't just choose the cheapest; try to find the product that is highest quality and best for you. This is an important preventative measure that can save you a lot of money and pain in the long run by avoiding cancer. If you need a sunscreen immediately and don't have time to conduct a lot of research, go for a cream that is SPF 30, broad spectrum, paraben free, with zinc oxide and no oxybenzone or retinyl palmitate.
Go to a store. Compare many different sunblocks. Decide which one best suits your needs. Make an informed decision.