Popular painkillers may be a poor choice for relief for people suffering from colds.

Researchers from Johns Hopkins University and the University of Adelaide in Australia found that two popular pain relievers - aspirin and acetaminophen - sharpened some viral cold symptoms and dulled the body's protective production of viral antibodies.The third most popular pain reliever, ibuprofen, had the same impact, but it was much weaker - perhaps to the point of insignificance.

Use of aspirin and acetaminophen might be only a minor irritant for most people with colds, the researchers concluded. The symptoms that are worsened can be improved with common cold medications such as pseudoephedrine.

The researchers warned of more serious hazards in the developing world, where children often suffer from life-threatening respiratory diseases that could be made more dangerous by use of the pain relievers.