The number is about 20 percent. Inhalants are the fifth most abused substance by teens, according to the Partnership for a Drug-Free America. Substances abused more often are marijuana, alcohol, cigarettes, and misused prescription drugs.

Some people view inhalant sniffing as a fad that will pass as teens mature.

Inhalants can cause death by starving the body of oxygen or forcing the heart to beat more rapidly and less smoothly. They can also cause severe damage to the brain and nervous system.

It is more common among younger teens. In a 2007 study, nearly 4 percent of eighth graders said they were current users of inhalants, the NIDA says. Only 1.2 percent of high school seniors said they were current users.

Teens can buy inhalants legally in stores. Inhalants are found in a variety of seemingly harmless products. As a result, teens who sniff inhalants to get high don't face the same supply problems that abusers of other drugs face.

Nitrous oxide is a colorless, sweet-tasting gas used by doctors and dentists for general anesthesia. It is called "laughing gas" because it often brings on a state of giggling and laughter. Nitrous oxide is abused when it is inhaled for its mind-altering effects. Inhaling the gas may starve the body of oxygen and can result in death. Long-term use can result in nerve damage.

Toluene is a solvent. It is a common ingredient in many paints, lacquers, glues, inks, and cleaning fluids. It is the cause of many inhalant abuse deaths and injuries. A study of 20 chronic abusers of spray paint found that even one month after no longer sniffing paint, 65 percent of the abusers still had damage to the nervous system. Such damage can affect perception, reasoning, and memory. It also can lead to poor muscular coordination and, eventually, dementia.

Volatile solvents are found in gasoline, paint thinner, spray paint, paint and wax removers, hair spray, odorants, air fresheners, cigarette lighter fuels, analgesic sprays, and gases used in aerosols such as whipped cream dispensers. Volatile solvents produce a quick form of intoxication. Many inhalant products contain more than one volatile solvent, so it is difficult to pinpoint the specific chemical responsible for brain or nerve damage or death.