Q: Our son vapes in his bedroom. Is it OK for him to use his e-cigarette when our dog Smoky is in his room?

A: No. E-cigarettes are electronic smoking devices, or ESDs, which heat, vaporize and emit numerous harmful chemicals that expose pets and people to substantial risk.

If your son must vape, he should do it outdoors to protect Smoky and the rest of the family from the ESD emissions.

The term “vaping” is a misnomer that implies ESDs emit harmless water vapor, when in fact, they discharge an aerosol filled with toxic chemicals at levels even higher than in tobacco smoke.

Some of these chemicals cause cancer and are reproductive toxins. Carcinogens in the aerosol include nitrosamines, formaldehyde, cadmium, lead and nickel.

When an ESD heats propylene glycol, a common ingredient in vaping liquid, it forms propylene oxide, a known carcinogen.

Exhaled ESD aerosol also contains nicotine. Research shows that nonsmoking bystanders absorb the same amount of nicotine whether they are exposed to secondhand ESD aerosol or tobacco smoke.

Aerosolized nicotine also adheres to surfaces where it promotes “thirdhand” exposure.

ESD aerosol contains higher concentrations of fine and ultrafine particles than tobacco smoke. These tiny particles are inhaled deeper into the lungs than the larger tobacco smoke particles, which increases the risk of developing severe lung disease.

Aerosols also contain flavorings such as diacetyl, a chemical linked to lung damage, and volatile organic compounds such as benzene, a poison in automobile exhaust.

Moreover, ESD aerosol contains carbonyls and other chemicals that cause heart attacks and other cardiovascular damage.

A study on the behavioral effects of secondhand vaping and smoking on dogs from 2,857 homes found significantly higher excitability and separation-related problems in households where someone vaped.

So, join the many national and international health organizations that recommend ESDs not be used indoors. If your son can’t stop vaping, ask him to vape outside and stay away from Smoky when he does.

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Q: Why do cats purr?

A: Your question has perplexed philosophers and cat lovers for centuries.

Cats purr when they are content and relaxed, often kneading with their front paws at the same time.

Paradoxically, cats also purr when their bodies are tense and they appear anxious or frightened — and even when they’re injured. So, purring may be, in part, a self-soothing behavior.

Females purr during labor, and mama cats purr before and during nursing. Since kittens are blind and deaf for the first two weeks of life, the mother’s purr vibrations may help them find their way to her milk and nurse more efficiently.

Kittens begin purring at 2 days old. By 3 weeks of age, they purr to litter mates, perhaps to alert them that Mom is available for nursing.

In adults, purring tells others that a cat poses no threat, which appeases a dominant cat and prevents an attack.

Purring occurs during both inhalation and exhalation when air moves through the glottis, the slitlike opening between the vocal folds, called vocal cords in humans.

The sound oscillations are controlled by the brain, diaphragm, throat and nerves that connect them.

Cats purr at a frequency of about 25 hertz, or 25 vibrations per second, with harmonic overtones at 50 and 100 hertz.

Vibrations of 18 to 35 hertz improve joint mobility. In many animal species, 20- to 50-hertz vibrations increase bone density, stimulate bone fracture repair and promote healing of injured muscles and tendons.

Frequencies of 50 to 100 hertz decrease pain in humans and may do the same for cats. Furthermore, 100-hertz vibration helps ease breathing in humans with chronic respiratory disease.

So, purring likely evolved because it gave cats a survival advantage. This magical healing system that has long perplexed us may even be the secret behind cats’ nine lives.

Lee Pickett DVM practices companion animal medicine in North Carolina. Click here to ask her questions for her weekly column. The opinions expressed are her own.