 Shopping for sunscreen is a complicated business. Even before you get to the big questions like do you go for the spray on stuff or the slap on cream? Does the issue of how safe the product is? And that inevitably leads to the question of whether you go for conventional sunscreens, the ones that use chemicals like oxybenzone or evo-benzone, or one of the newfangled nanoparticle sunscreens. And if you do go nano, just how safe are those tiny little particles you're about to spread on your skin? Nanoparticle sunscreens use microscopically small particles of zinc oxide or titanium dioxide. You can usually tell if a sunscreen uses nanoparticles because it lists one or both of these materials on the label. Companies have been using these substances for a decade or so now claiming that they make for a better sunscreen, but for some users there are lingering doubts about their safety. So what do you need to know when deciding whether to go nano or not before braving the sun's rays? Here are five things that may be helpful. 1. Nanoparticles in sunscreens stay on top of your skin and don't pass through it. When manufacturers started to use these miniscule particles, researchers wondered whether they could in fact slip in between your skin cells or even get into the cells themselves. Fortunately, after several years of research it looks like healthy skin is great at preventing nanoparticles getting into your body. 2. Nanoparticles in sunscreens work by reflecting harmful ultraviolet light away from your skin while allowing visible light through. Because of this they create a barely visible protective barrier, which is great if you'd rather not look like you've just been whitewashed. What's more they protect you as soon as they've been applied, unlike many of the more conventional sunscreens that need time to settle into your skin before they're fully effective. 3. Uncoated nanoparticles of titanium dioxide and zinc oxide can produce harmful chemicals called free radicals when exposed to sunlight. To avoid this, sunscreen manufacturers coat them with a thin layer of materials like silica or alumina. The layer prevents free radical formation and transforms potentially harmful particles into safe ones. 4. Non-nanosunscreens may be more harmful than nanosunscreens according to some research. Conventional ingredients like oxybenzone may lead to allergic reactions with some people, and small quantities can penetrate through your skin and into your body, where there's a chance that they may cause problems by behaving like human hormones. In contrast, at this point there is no evidence that nanoparticles behave similarly. 5. Inhaling large quantities of titanium dioxide and zinc oxide nanoparticles probably isn't a good idea. Research has shown that even though these substances are likely to be okay if inhaled in small amounts, smaller particles definitely do do more damage than larger particles if they get into your lungs. So you might just want to watch what you're breathing while using one of those spray on nanosunscreens. Finally, whether you end up opting for nano or non-nanosunscreens or using some other form of protection, remember that exposing unprotected skin to the sun's UV rays is one option that is definitely not safe here. If you have any thoughts on nanosunscreens or sun protection in general, please do join the conversation in the comments, and remember to check out the additional resources in the blurb below.