Why You'll Want To Cut An Onion Before Painting A Room

One of the worst parts about painting a room isn't the cramping hands, dirty floors, or rogue drip marks. Instead, it's the headache-inducing vapors that linger in the space for a few days before dissipating. These vapors are Volatile Organic Compounds (VOCs), which are the gases that release when the paint dries (via Country Living). To lessen their effect, paint can labels recommend that users only paint in a well-ventilated room. That means throwing open doors and windows. Some people take it further and run fans or air purifiers to get the room to air out faster, but that telltale smell still lingers. 

If you want to speed up the process, you should cut an onion before you paint a room. While it sounds like an old wive's tale, an onion can help neutralize harmful paint smells, allowing you to use the room again much faster. Since most people already have an onion in the kitchen at any given time, it's a paint hack that's definitely worth trying. 

How to use an onion to air out a room

If you're extra sensitive to paint smells, or simply want to air out the room quicker, all you need is an onion to get the room back to normal. Take one white onion, slice it in half, and put it on opposite sides of the room. You don't want to put the two halves right next to each other, or else you'll have them both working to purify that one area of the space. By putting them on opposite ends, the air quality on both sides of the room will be cleaned. If you painted a bigger room, such as the living room or primary bedroom, consider cutting more than one onion. 

However, you should skip this hack if you have curious cats or dogs. Onions are toxic to both pets, so you will end up at the vet if you leave them in an easy-to-reach area, such as the floor or windowsill (via Bloorcourt Veterinary Clinic). In that case, it will be safer to use baking soda to air out the room.

Why this works

Onions are naturally absorbent, which is why they can help neutralize paint odors. It's the same reason why some people swear putting a cut onion in a stinky shoe cabinet can help absorb musky odors — it's a smell buster. But the exact science behind why onions wipe away paint fumes, in particular, is interesting.

Chemicals known as aldehydes are what give paint that acrid smell as it dries. "These aldehydes have a low odor threshold, which means humans can smell them at low levels, often a few parts per million," chemist Nathan T. Allen, Ph.D., told My Chemical-Free House

But the chemical that makes you cry when cutting onions — Syn-propanethial-S-oxide — neutralizes aldehydes, making them disappear from the air. "Because the aldehyde is at such a low level, it doesn't take much of the Syn-propanethial-S-oxide to react with a substantial portion of it," Allen went on. "Let's just say the onion smell bleaches the smell of paint." So if you have a few onions in your pantry and are painting, cut up some halves to keep paint fumes at bay!