Sit, speak, and play dead -- dogs can learn plenty of tricks, if you're willing to take a little time to teach them.

But the best trick of all comes naturally: Pets can chase away asthma and allergies the way a guard dog can scare off burglars -- and it doesn't take a loud bark or a lot of teeth.

In fact, even a lazy old cat has this power -- because kids born to mothers who had pets during pregnancy have lower levels of the IgE antibodies linked to allergies and asthma.

Researchers at Henry Ford Hospital in Detroit tested those antibody levels in 1,187 babies at birth, six months, and two years, and found that the kids who had prenatal pet exposure had up to 33 percent fewer than children from petless homes.

The biggest benefit went to children of European, Asian, or Middle Eastern descent, who got the full 33 percent drop.

For black children, the difference was only 10 percent -- but still enough to put them at least a baby step ahead of asthma and allergies, and that's nothing to sneeze at.

Babies born vaginally to women with pets also got a bigger boost, with IgE levels 16 percent lower than C-section infants.

In other words, pets don't always cause allergies and asthma -- and they might even prevent them.

But while that means Spot can "stay" in homes with a new baby, there is one threat even the roughest, toughest Rottweiler can't chase away: mold.

Having this stuff around the house could lead to a childhood of breathing misery.

Researchers examined data on 176 children who were believed to be at high risk for asthma because of a family history of the disease. They also used a test called the environmental relative moldiness index, which measures levels of 36 different types of mold to create an overall "mold burden."

And that mold brings some burden. Kids from homes with the highest mold burdens were three times more likely to come down with asthma during the seven-year study period than kids with little mold exposure.

The researchers wrote in Annals of Allergy, Asthma & Immunology that parents of kids at risk for asthma should make sure they find and fix water damage and get rid of all the mold -- which is pretty good advice for everyone else, too.