Sir, I have suffered from acne rosacea for 8 years. I was prescribed and have been taking both erythromycin and doxycycline. My concern is the effect of taking these antibiotics over long periods. I heard recently that it may reduce my immunity to cancer. Could you please give me your comments?

Your concerns are well founded, but for a reason that has little to do with cancer. These antibiotics (especially the doxycycline) have a broad spectrum of activity against bacteria in your body. This could lead to the development of resistance should you ever need to receive treatment for an actual infection. As an example, drugs of the family of erythromycin are often used to treat infections of the throat, ears and sinuses. One of the drugs, azithromycin, can be taken as two pills once a day for three days as the TOTAL treatment for the infection. It may be that because of the long-term use of erythromycin, the bacteria in your throat may be resistant to the azithromycin and you would lose access to this easy and effective treatment.

There are local treatments for rosacea (metro gel, vitamin A, etc) that may be effective and avoid the use of systemic antibiotics.