Poisoning is the most common cause of nonfatal accidents in the home. Fewer than 3,000 of the more than 12 million known chemicals are responsible, but almost any substance ingested in large quantities can be toxic.

The following substances are frequently involved in accidental poisonings in the home:

• Acetaminophen -- More than 100 products (such as Tylenol) containing acetaminophen are available without a prescription. Acetaminophen is very safe when used as directed, but can seriously damage the liver in large quantities, often causing death.

• Aspirin -- Aspirin is not recommended for children and teenagers because it has been associated with a condition called Reye's syndrome in this age group. Poisoning is most severe in children who have been taking high doses of aspirin for several days. The most toxic form of aspirin is oil of wintergreen (methyl salicylate), a component in vaporizers and liniments.
• Caustic substances -- Swallowing caustic substances (such as drain cleaners or dishwater detergents) can damage the mouth, esophagus, and stomach.
• Lead -- Lead poisoning is usually a chronic disorder, with exposure accumulating over time. Many children are exposed by swallowing lead-based paint chips, but people may also be exposed by swallowing any lead object, such as BBs and fishing weights. Foods stored or served in lead-glazed ceramic ware may be contaminated. Exposure to the fumes of leaded gasoline is another source.
• Iron -- Even a few iron supplements intended for adults can be harmful to children.
• Hydrocarbons -- These are found in petroleum, natural gas, and coal. Every year, more than 25,000 children under the age of 5 are poisoned by swallowing gasoline, kerosene, antifreeze, and paint thinners.

Such poisonings in the home are preventable. The Merck Manual of Medical Information offers these tips for protecting your family:

• Use safety caps and containers.
• Store dangerous substances in locked cabinets.
• Don't store household products on lower shelves.
• Keep drugs and dangerous substances in their original containers.
• Teach children about the dangers of eating or touching drugs and household products.