DEAR DR. DONOHUE: At my urging because of a strong family history of colon cancer, my 30-year-old son had a colonoscopy. He had four tubular adenomas — a surprise to us and the doctor. The doctor suggests a repeat colonoscopy. Please explain the different types of polyps. Don’t all polyps become cancerous if not removed? – E.T.

ANSWER: A polyp is a growth that springs from the outermost lining of hollow organs. Polyps arise in the nose and sinuses, but I am going to speak only of colon polyps.

There are two major types of colon polyps. One is a hyperplastic polyp, and it is almost never a cancer threat. The other is an adenoma. More than 90 percent of adenomas do not become cancerous, but the remaining 10 percent can turn into cancer. By looking at a polyp, the doctor cannot tell if it is a dangerous one; it must be examined microscopically. Up to 40 percent of people older than 60 have at least one colon polyp.

Adenoma polyps larger than 1 cm (two-fifths of an inch) raise the suspicion of cancer and the more numerous are the polyps, the greater the cancer threat.

Adenoma polyps are further subdivided according to their appearance. Ones that look like drinking straws with a round cap on one end are tubular adenomas, the most common kind, and the least likely to become cancer. Villous adenomas resemble a tiny cauliflower and are most likely to turn into cancer. Tubovillous adenomas are a cross between these two and have an intermediate cancer threat.

If no adenoma polyps are found, then the next colonoscopy can wait for 10 years. One or two low-risk polyps should call for a repeat colonoscopy in five to 10 years. If three to 10 polyps are found, then colonoscopy should take place again in three years. More than 10 polyps require an examination sooner.

Large polyps, polyps with microscopic evidence of precancer changes and people with a family history of colon cancer have to be judged individually for the next scope examination.

Readers can obtain the booklet covering colon cancer, its detection and treatment by writing: Dr. Donohue, No. 505, Box 536475, Orlando, FL 32853-6475. Enclose a check or money order (no cash) for $4.75 U.S./$6 Can. with the recipient’s printed name and address. Please allow four weeks for delivery.

DEAR DR. DONOHUE: For years and years, I have been taking kelp tablets because a friend convinced me they are good for the thyroid gland. I wonder if they are. Am I helping or hurting myself? – B.Z.

ANSWER: Kelp is seaweed. It has high iodine content. In former days, there were many parts of the globe where soil, and therefore food raised on that soil, had low iodine content. Populations in those areas developed thyroid disorders like goiters. Many infants born there had severe physical and mental developmental problems. Now, with the knowledge of iodine deficiency, those populations are provided other sources of that mineral. In many countries, iodine is added to salt.

The daily adult requirement of iodine is 150 micrograms. A microgram is much smaller than a particle of dust. The daily upper limit for iodine is 1,100 micrograms.

If you’re not exceeding the daily upper limit, you’re not hurting yourself. However, I don’t believe you’re benefiting yourself significantly.

DEAR DR. DONOHUE: I am a 13-year-old girl with red hair and lots of freckles. I hate the freckles. How can I get rid of them? Is there something I can put on them? How about a vitamin? – D.O.

ANSWER: Freckles appear because of the genes you inherited from your parents and because of exposure to sunlight. You can’t do anything about your genes. You can do something about sunlight. Before going outside, apply sun-blocking lotion or cream. I bet after a winter of staying mostly indoors your freckles have faded considerably. You can keep them that way by always wearing sun-block. Vitamins won’t help.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475. Readers may also order health newsletters from www.rbmamall.com