Researchers at Tufts Medical School discovered in 1987 that plastic containers contain cancer-causing chemicals that can leach into your food. Not all plastic is alike, so use this handy guide to protect yourself.

Look at the recycling number on the bottom of your container with the little triangle around it to determine what is safe and what should be avoided.

Safest: 1 or 2 on the bottom. These are clear and cloudy water and milk containers called PETE and HDPE. They are safe for storing food and drink, but DON'T MICROWAVE THEM.

Generally Considered Safe: 4 or 5 on the bottom. Use these sparingly, and DON'T MICROWAVE THEM.

Most Dangerous: 3, 6 or 7 on the bottom. They contain the most volatile chemical called BPA, and should be avoided at all costs.