Wanting to recycle as much as possible is a great instinct, but it’s very important to know what should and shouldn’t go in the bin or to the recycling center. Though recycling technology and techniques are continually improving, there are many things that we simply aren’t able to recycle yet, and others that are too hazardous to be worth the risk. Here’s a list to get you started and help you remember: when it comes to recycling, more isn’t always better.

Pizza boxes

Because the vast majority of pizza boxes are contaminated with grease or other food waste, they should never go in the recycling bin. Those food remnants contaminate other paper and cardboard items they’re recycled with and can end up turning valuable recyclables into unusable waste.

Anything with Food Waste on It

The same goes for other containers or items that come into contact with food. Bottles, jars, and other plastic food containers (as long as they’re marked as recyclable) should always be cleaned out first. You want your recycling to reduce waste, not produce more.

Wet Paper Products (Including Wet Cardboard)

Paper products that are already wet start to break down before they make it to the plant, so they can’t be processed like the dry stuff. Wet paper is also likely to be contaminated, which presents the same problems that come with the first two items on our list.

Receipts

Most receipts are printed on thermal paper that has been found to contain BPA, a potentially dangerous compound that can end up in the new recycled paper and could also make its way into the environment to harm plants and animals.

Cling Wrap

It’s usually contaminated with food, and it can clog machinery at the recycling plant. So if you can—don’t use it at all. Stick with reusable containers as much as possible).

Medical Sharps

Things like needles, syringes, and lancets must be disposed of properly for the sake of safety. They should never be tossed in a trash can or recycling bin where they might injure or even infect others in your home or waste collection and processing staff. Find out how to dispose of these items safely. The FDA and other diabetes information sources can help you learn to be smart about disposing sharps.

Ceramics

By nature, ceramic materials like coffee mugs and pottery can’t be melted down, so they can’t be processed into something new the way other recyclable materials can. But just because it can’t go to the plant doesn’t mean it has to go to the landfill: old ceramics are great materials for upcycling projects. There are more items and materials that can’t be recycled (yet), so make sure you check for markings that let you know a product is recyclable, make sure they’re clean before you put them in the bin, and know what items your local recycling facility can and can’t process. That way, you know you’re sending them materials that they can really use.