The fact that researchers have sequenced the genomes of all 99 strains of the human rhinovirus is cold comfort for my raw nose.

　　Even if drug makers can someday create antiviral drugs that attack common weaknesses in those strains, many unrelated viruses also cause symptoms we associate with colds. 'It's like wanting a cure for everything that causes red spots on the skin,' says Ronald Eccles, director of the Common Cold Centre at Cardiff University in Wales.

　　In fact, what we experience as a terrible cold isn't the virus itself -- it's the body's immune system going into chemical overdrive to help flush out the infection.

　　One key chemical, called bradykinin, stimulates the nasal membranes to make runny, watery mucus and activates nerve endings in the throat, making it feel scratchy and sore. Bradykinin also sparks inflammation that swells blood vessels in the nasal passages, causing congestion. And cytokines, released by white blood cells, set off the fever, headache, muscle ache and loss of appetite. Scientists have tried to develop antagonists to those chemicals, without much success.

　　Curiously, this cascade of chemical misery happens only with a minority of cold viruses. For every cold we know of, virologists say, we fight off three or four with no symptoms.

　　Why some set off a nasty immune response and others don't is a mystery -- probably involving the genetics of the virus and the patient, and the patient's overall health, says Stephen B. Liggett, a physician-scientist at the University of Maryland Medical Center and senior researcher on the rhinovirus project.

　　People who sleep less than seven hours a night are far more likely to develop symptomatic colds than those who get at least eight hours, according to a recent study in the Archives of Internal Medicine. Another study in the same journal found that people with low levels of vitamin D are also more susceptible to colds.

　　Stress makes colds worse -- probably because it increases corticosteroid hormones, which lower resistance to infection. 'It's not just big stresses like bereavement or losing your job,' says Prof. Eccles. 'Having a bad hair day, losing your car keys -- those can get you stressed and sick.'

　　The notion that chills lead to bad colds was debunked years ago, but it may be due for rethinking. In 2005, researchers at the Common Cold Centre chilled the feet of 90 volunteers in ice water, and found they developed twice as many colds as students whose feet hadn't been chilled. Prof Eccles theorizes that the sick students had asymptomatic viruses that turned symptomatic when the chill constricted blood vessels in their nose, allowing the viruses to replicate. He recommends keeping the nose covered up in the cold.

　　There's no evidence that treating symptoms affects recovery time, experts say. It takes from five to 10 days, no matter what you do, so focus on comfort. Best bets are pain killers like acetaminophen, hot drinks and decongestant sprays, says Prof. Eccles. Dr. Liggett says standard antihistamines that dry mucous membranes can make nasal obstruction worse, and there's no proof that mucolytics -- cough medicines -- help much. Nor is there convincing evidence that vitamin C, nasal zinc or echinacea can help ward off a virus.liuxuepaper.com