We're all big fans of buying used items [1]; it's a great way to save money and be environmentally friendly. Still, there are certain things you should be wary about buying secondhand because some of them may even be hazardous to your health (or just gross). Here's a list:

• Bike helmets: You may buy a used bicycle helmet that seems brand new, but sometimes the real damage can't be seen. Some helmets crack in just one hard blow, so you need to make sure that it hasn't already done so, or it may not be able to absorb the impact of subsequent hits. It's best to be safe and buy a new helmet in good condition.
• Swimsuits: Other than the uncomfortable fact that the previous owner didn't wear underwear with the swimsuit, there's also a lot of stretching that goes on if the suit has been used. It can lose its shape over time, so it may be better to purchase a brand-new one.
• Mattresses and pillows: You don't want to think about what kind of mites are living in a used mattress and pillow — not to mention mold, bacteria, and bodily fluids. Further, mattresses have a shelf life of five to seven years, and it won't be able to provide the same quality of comfort and support beyond that, so you might be better off going with new bedding.
• Baby cribs and car seats: You can't be sure a used crib or car seat is safe because there are plenty of product recalls that you may not be aware of. The safety standards are updated all the time, so the used item may not meet the current safety requirements. Put your child's life in the care of a new, certified product.
• Tires: Although a used car can often be a good buy, used tires are another matter. Worn tires are dangerous in wet conditions and will give you less grip on the roads. Be cautious when purchasing tires.
• Shoes and sandals: You need to be careful when buying footwear because the shoes may have already molded to the previous wearer's foot. Shoes that don't fit well can cause discomfort and pain in your feet, and they may even lead to back problems.
• Nonstick cookware: Nonstick pots and pans that have chips or scratches on them should be thrown away and not resold. Cancer-causing chemicals beneath the surface of this cookware could start making their way to your food with damaged pans, so ditch the risk.