Doctors also advise against taking non-steroidal inflammatory drugs (NSAIDS).

In both cases, these drugs can cause severe reactions. Paracetamol has been recommended as a safe alternative.

Researchers compared the use of aspirin and paracetamol by 664 asthmatics and 910 people without asthma over a period of 12 months.

The study participants were aged between 16 and 49, and drawn from 40 general practices in south London.

Frequent use of paracetamol was also associated with more severe asthma, and with inflammation of the lining of the nose (rhinitis).

Very few asthmatics were taking paracetamol frequently for asthma symptoms.

Body changes

The authors suggest that frequent use of paracetamol decreases circulating levels of the antioxidant glutathione, high levels of which are found in the lining of the airways and the nose.

Glutathione is thought to protect the lungs from the harmful effects of pollutants and free radicals.

Free radicals are charged particles that damage the tissues of the body. They are found in high levels in the lungs of asthmatics.

The authors warn that their findings should not encourage asthmatics to switch from paracetamol to aspirin or NSAIDS, as this could be dangerous.

But they do suggest that, if possible, asthmatics who regularly take paracetamol should try to cut down their use.

'Adults only'

The National Asthma Campaign issued a statement stressing that the study related to adults only.

The statement said: "This study suggests that daily use of paracetamol may be linked to a higher possibility of the worsening of asthma symptoms in adults.

"It does not show that paracetamol is linked to any increased chance or risk of developing asthma.

"In both children and adults, the patient information provided with this type of medication states that it must not be given for more than three days without consulting a doctor.

"Always consult your doctor or pharmacist for advice when giving painkillers to your children, especially if they are currently taking any other treatments - either prescribed or over the counter medicines."

Aspirin should not be given to children because of the risk of Reye's syndrome, a rare but potentially fatal condition.

The research, by the Department of Public Health Sciences, Guy's, Kings' and St Thomas's School of Medicine, London, is published in the journal Thorax.