Dear Dr. Douma: Three years ago, I had tenacious phlegm that I'd have to work very hard at to hack up and spit out. After a lot of tests, including allergy testing, scoping, MRI and X-rays, nothing was found, but it went away.

Although I have not smoked for 40 years, it is now returned and I need help to figure out how to be able to get the phlegm out. - J.D., Holbrook, N.Y.

Answer: Coughing is a complicated but important reflex to protect the lungs and airways against foreign particles. Any irritation of the airways and bronchioles in the lungs will likely cause excess secretion of bronchial mucus. Sputum is a mixture of the foreign particles, mucus and cells expelled by the lungs.

An unusually large amount of sputum is also called phlegm, which is a sticky, viscous secretion produced by the mucosa of the respiratory passages and is discharged through the mouth.

You are right to try to bring up the phlegm to clear your airways. Coughing that brings up a lot of phlegm probably should not be suppressed.

While I appreciate your concern and interest in finding a way to clear the phlegm, the best course is to keep it from forming in the first place. So the first step is to identify the source of the problem.

Examination of the phlegm produced can be helpful. A yellowish, green or brown appearance suggests infection. Clear, white or watery phlegm suggests a viral infection, allergy or irritant as the cause. A microscopic examination of the phlegm may show evidence of bacteria and white blood cells, another indication of infection.

Unless your environment (home, workplace) or the time of the year has changed between the time your phlegm production went away and the time it came back, it's less likely that your problem is caused by allergy.

Allergic reactions do not usually come and go as you have described. Do you have peaks and valleys of phlegm production now? You might test this allergy theory by taking some antihistamines for a while and see if your condition improves.

The fact that the increased phlegm production went away for a while then came back suggests to me an infection. You did not mention having any pain when coughing, so your lungs and airways are probably not inflamed.

You can test this infection theory by taking a course of antibiotics when the phlegm production gets really bad. If the antibiotics help dramatically, you probably have a bacterial infection, at least as a complication. Standard antibiotics are not effective against viral infections, however.

Antibiotics are prescription medications, so you will have to see a health care provider. While you are there, ask if a laboratory examination of your phlegm is appropriate for your particular situation.

Although you have not smoked for 40 years, the damage done when you were younger can be a factor even today. And for those who have recently quit or continue to smoke, the situation is often much worse.

Update on Multiple Sclerosis:

MS and diabetes may have a common immunological pathway, but the autoimmune process in each disease ends up attacking different cells of the body.

In research reported in the Journal of Immunology, immune cells in people with MS targeted antigens that are found in people with autoimmune diabetes.

The researchers also found that injection of a toxin produced by the pertussis virus into mice created a disease that acted like MS in humans. Pertussis was a very common infection, which has diminished dramatically since a vaccine - DPT - has been available.

Two findings from this study may be a possible cause of MS by pertussis and a better understanding that, like diabetes, there is probably a long time during which MS is developing prior to any symptoms. For both diseases, early detection may lead the way to treat before the disease process has been fully established and before irreversible damage has been done.