DEAR DR. DONOHUE: My 12-year-old boy came down with scarlet fever, and it scared me to death. I remember my mother speaking of quarantines for every member of a family where there was a case of scarlet fever. My doctor took this whole thing very nonchalantly and treated him with penicillin at home. Should more have been done? – Y.P.

ANSWER: Scarlet fever is a strep throat with one slight addition. The strep germ of scarlet fever releases a substance that brings on a skin rash. That’s the only difference, and it does not make scarlet fever any greater a threat than is strep throat.

The skin has a diffuse redness, the “scarlet” of scarlet fever. The face is flushed except for a band of white skin above and below the lips. As the days pass, the skin develops a sandpaper feel. The tongue can become as red as a strawberry. Skin redness disappears in six to nine days, and then the skin peels as it does after a sunburn.

Aside from the rash, the symptoms of scarlet fever are the symptoms of a strep throat. There’s pain on swallowing, swollen neck nodes, a rise in temperature and often a headache.

Penicillin is the treatment for both strep throat and scarlet fever. Both can be treated at home.

Both illnesses can resolve on their own. But left untreated, either can evolve into rheumatic fever. The five prominent signs of rheumatic fever are heart and heart valve involvement, joint swelling and pain, pea-sized nodules under the skin, a peculiar rash and uncontrollable thrashing of arms and legs. Not all these signs need be present to qualify as rheumatic fever. Some are seldom seen, an example being the arm and leg thrashing, which is known as St. Vitus’ dance. Penicillin treatment prevents this complication.

Quarantines are a thing of the past for this illness.

DEAR DR. DONOHUE: Please answer a question about vitamin D and sunlight. I understand that the vitamin comes from sun shining on skin. I live in the far north and am inside much of the winter. How much sunlight do I need to keep up my supply of vitamin D? – I.K.

ANSWER: Ultraviolet light from the sun converts certain substances found in the skin to vitamin D.

North of 42 degrees latitude – and that takes in much of the northern United States and all of Canada – a vitamin D deficiency can occur in those who are housebound all winter long. In Boston, at the end of the 2003 winter, men between the ages of 18 and 29 were tested for their vitamin D levels. One-third were found to have low levels of vitamin D. If this happens to active young men, you can imagine what happens to the housebound elderly.

Some foods – dairy products, principally – are fortified with vitamin D, but people get 90 percent of the vitamin from the action of sunlight on skin.

The amount of sunlight needed for skin production of vitamin D depends on the time of day, the season, the geographic location and the amount of skin exposed to the sun. Roughly, people need 15 minutes of sun exposure that strikes the face, arms and hands between the hours of 11 a.m. and 2 p.m. at least two or three times a week to sustain their supply of vitamin D.

It is justified for many people, especially those who seldom get outside in the winter, to take a daily supplement of this vitamin.

DEAR DR. DONOHUE: Do doctors routinely take children’s blood pressure? I have twin girls who are 5, and they never have had their blood pressure taken. They see the doctor every year for a physical. – R.K.

ANSWER: Doctors should begin taking children’s blood pressure by age 3. Children rarely have elevated pressures, but when they do, the elevation often points to an underlying problem that’s causing the pressure rise. A malfunctioning adrenal gland or serious kidney problems can elevate blood pressure. Such high blood pressure is called secondary hypertension. The rise is secondary to a problem in another body organ.

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.