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Gupta: Smoking may negate allergy benefit of pets

Dr. Sanjay Gupta

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Dr. Sanjay Gupta

(CNN) -- Past research has shown that children who grow up with pets in their homes have less chance of developing common allergies. But a new study finds that parental smoking negates any allergy benefits of pets.

CNN medical correspondent Dr. Sanjay Gupta explained the details with anchor Soledad O'Brien.

GUPTA: Good morning, Soledad.

[This is a] big topic, especially this time of year, with 40 [million] to 50 million Americans suffering from significant allergies. People were encouraged a couple of years ago -- there was a study that came out looking at household pets and the possible protective effects it may have on children developing allergies later in life.

The study basically said that children with two or more pets, whether they are dogs or cats, reduce allergies by up to 50 percent. Those sorts of allergies were from dust mites, grass, ragweed, things like that.

Now a follow-up study, just coming out this weekend, talking about negating those protective effects by parents who smoke. Children with parents who smoke regularly lost the protective benefits of pets. Those were all negated if either one or both of those parents smoked.

Now this has been a point of some speculation for some time. Obviously, secondhand smoke is bad for you, but to actually draw a cause and effect that if the parents smoked, they actually would negate the effects, the beneficial effects of those pets in terms of allergies, this is sort of new stuff.

If both parents have significant allergies, then your child has about a 50 percent chance of developing allergies him or herself. If one parent has significant allergies, about a 25 percent. Not a huge surprise here, Soledad, that smoking, secondhand smoking, is bad, but this protective effect gone if the parent smokes [is more surprising].

O'BRIEN: Can you explain how the exposure to allergens ahead of time will actually protect children from getting allergies? That seems almost counterintuitive.

GUPTA: Yes, you know, this is interesting, and this is sort of the basis on which allergy shots are based, all sorts of things. A rule of thumb here: If you introduce allergens and you introduce them early in life, you may develop a protective effect later on in life. In the case of pets, about 50 percent.

Here's how it might work. Basically, the immune system favors allergies. So you know, when your baby is developing, when a child is developing, they favor allergies. They're looking for those sorts of things. So if you naturally expose them to the bacteria or other allergens, they're going to start to recognize those things, and next time they come knocking on the door, they're going to say no, we're not going to accept it this time, and basically the body becomes conditioned against those allergies. So a little bit of exposure early on may condition the body, so to speak, so the next time the allergy is seen, the body won't react to it.

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