There’s a big wide world of beauty products out there, and not all of them are your friends. In the last few weeks, we’ve talked about how to find products that complement your hair type. This week, we’re telling you about some ingredients in products that don’t complement anyone, least of all extension-wearers. So here are those chemical names, decoded, so you can start getting to know those ingredients labels a bit better.

Sodium Lauryl Sulfate/Sodium Laureth Sulfate. You’ve definitely heard of this one before. Sulfates are the number one ingredient you should be avoiding if you’re wearing hair extensions because they dry out your hair like crazy. Ideally, though, everyone should avoid the stuff if they can help it. They strip the natural oils off of your head, preventing the healthy distribution of said oils to the lengths of your hair. NOT recommended if you want well-hydrated hair.

Isopropyl Alcohol. We’re looking at you, hairspray. Isopropyl alcohol (otherwise known as rubbing alcohol) is another ingredient that can seriously dry out hair, and it’s found in a disheartening number of products designed to keep your hair in place. In large quantities or concentrations, this ingredient can even dry hair out to the point of breaking off.

Propylene Glycol. Products that come out of the bottle as a foam or emulsion more likely than not contain this chemical. It’s an anti-freeze that contributes to the liquid state of a product, and opinion is divided on the relative toxicity of the chemical. In general, concentrations of propylene glycol used in cosmetics are considered safe, but we recommend that those of you with sensitive or damaged skin, eczema, or other skin conditions refrain from using products with this ingredient, as it can cause allergic reactions.

Petrolatum/Mineral Oil. These ingredients form a plastic-y film around your hair strands in order to seal in moisture, but the barrier is so effective that your hair basically can’t breathe through it. This can ultimately impair hair growth.

Ethanolamines (DEA/MEA/TEA). These guys are supposed to emulsify your products (make them foam) and help maintain a healthy pH level in your hair and scalp, but they have the unfortunate side-effect of drying your hair and skin out. More importantly, they’ve also been linked to cancer!

Formaldehyde, Formaldehyde-donors, and Parabens. We’re lumping all of these ingredients together, even though they definitely have some differences. Formaldehyde is supposed to temper the carcinogenic properties of other ingredients, formaldehyde-donors are chemicals like ureas and DMDM Hydantoin that act as preservatives in beauty products, and parabens are antimicrobial preservatives. What these guys all have in common is a potential link to cancer and immune-system problems. As much as we love beautiful hair, it’s not worth compromising your overall health to achieve it.

Fragrance. If you see “fragrance” or "perfume"/"parfum" on the label of a product, that’s basically code for “and many other chemicals we won’t list here.” Skip the ambiguity in favor of an unscented blend. If you really can’t deal without your signature hair scent, try to recreate it with essential oils.

Need help sorting out which hair (and skin) products are safe to use on your body? EWG’s Skin Deep Cosmetics Database has proven invaluable for us, and we think it can help you out, too. Try it out, and let us know what you think!