In the good old days, most of us used newspaper to get that fire started. Now, if you’re like most Americans, instead of a stack of newspapers you’ve got a tower of cardboard shipping boxes.

And if you have a fireplace or wood stove, you may be tempted to kill two birds with one stone. After all, cardboard certainly is flammable and that fire isn’t going to start itself.

Not so fast. As it turns out, those shipping boxes may be hazardous to your health.

Cardboard is often treated with chemicals. Burning it could release hazardous fumes. Also, once ignited, cardboard tends to float up with the flames. That’s not only a fire hazard in your house, should it get past your screen, but outdoors as well — that burning cardboard could travel up the flue and out the chimney.

Newspaper is still a good option, but in this digital age subscriptions are down and supply might be scarce. There are a lot of effective fire-starters on the market, but beware of those packed with chemicals that could be hazardous to children and pets. You can search for natural options online (which might add to your shipping box collection) or you can step outside, get some exercise and fresh air while gathering up natures kindling: dry pine cones, twigs and bark.

Finally, at the risk of putting a damper on that cozy fire, you should probably skip it altogether if you’ve got someone in the house with heart or lung disease.

“Smoke from wood-burning fireplaces and stoves, especially less efficient units, contains particles that can trigger exacerbations (or attacks) of asthma, COPD and chronic respiratory conditions in general,” says Dr. Robert Bundy, a pulmonologist with Hartford HealthCare Medical Group in Willimantic. “These fine particles can even aggravate cardiovascular diseases in high risk patients, with the potential for triggering heart attacks with heart failure, irregular heart rhythms, and possibly stroke.”