Many of us remember that one relative growing up who would sneak outside during the family holiday gathering to light up a cigarette. “Don’t smoke, kid,’’ they would say, in between puffs.

But even though smoking rates have been dropping in recent years, simply not picking up the habit or keeping your distance from someone who is smoking won’t keep you safe from all of tobacco’s harmful effects.

According to a study published in the journal Science Advances, third-hand smoke is a little-known danger. This happens when cigarette smoke sticks to places you wouldn’t expect, and it can be just as harmful as second-hand smoke.

Research shows cigarette smoke can travel through the air and stick to walls, clothes and furniture. Even six months after smoking was banned in casinos, heavy smoke residue remained on the walls and carpet. Even worse, smoke can find its way from outdoors into buildings and circulate throughout central air-conditioning systems.

Unfortunately, young children could have increased exposure to these harmful chemicals, since they tend to crawl around on the floors and put random objects in their mouth. Children from low-income families could be affected the most, since studies show more than 25 percent of people below the poverty line smoke.

Although it’s unrealistic to expect everyone to quit smoking, and we certainly can’t always remain inside the comfort of our smoke-free walls, third-hand smoke can be eased by airing out and thoroughly cleaning rooms and carpets.

So, the next time Uncle Billy tries to sneak a smoke in your basement, send him outside or air out the room.