DEAR DR. DONOHUE: When I was in my 20s, I had a very bad reaction to a tetanus shot. My arm and neck swelled. I had to be packed in ice. I was told that I was allergic to the tetanus shot and never to get another one. I am now 85 and would like to know if I should get more tetanus shots. – D.B.

ANSWER: Tetanus (lockjaw) is uncommon in the United States and Canada, but for the few who get it, it is a dreadful infection. (Worldwide there are more than a million cases yearly.) The germ that causes it lives throughout the world in soil and in the intestinal tracts of many animals. Puncture wounds – such as those from the always-quoted example of a nail on the barnyard floor – introduce the germ into the body, where it produces a poison, a toxin that causes painful, prolonged and intense muscle spasms. Contractions of the chewing muscles lock the jaw tightly closed. Spasms of the back muscles cause the body to arch in an agonizing contortion. During all this, the patient is fully alert and conscious.

Getting immunized against tetanus is a lifelong affair. Adults should be revaccinated every 10 years. Although there are only a few cases of lockjaw here, most of them occur in older people whose immunity to the infection has waned because they have let their vaccinations lapse.

Do you know what kind of tetanus shot you had back then? Sixty years ago, when you got that shot, there was a tetanus treatment made from horse serum. This wasn’t a vaccine. It was a shot used when a person might have had an exposure to tetanus – a prophylactic shot. The horse-serum shot caused many allergic reactions. It is no longer used. Now that prophylactic shot is prepared from human serum.

The tetanus vaccine is not commonly responsible for severe allergic reactions. If it does cause them, then a person is left with only one option – scrupulously cleaning any soil-contaminated wound with copious amounts of soap and water. That might be the route you are forced to take.

DEAR DR. DONOHUE: I went to a doctor to have some growths removed from my body. She told me they were seborrheic keratoses. Is that a disease? She never told me what to do about it. Do I need medicine or vitamins? I am 78 years old. – L.J.

ANSWER: If you define a disease as something that makes people sick, seborrheic keratosis is not a disease. Almost every older person has at least one seborrheic keratosis, and most have many. My skin is a particularly fertile soil for cultivating them.

They come in all shapes and sizes. They can be as small as eight-hundredths of an inch to larger than 1.2 inches in diameter. The color most often is tan or brown, but it can vary, along with the size. So can the texture. Most of the time their surface is rough and cracked, but on occasion it’s smooth. They look like they’ve been pasted on the skin.

They aren’t cancer, and they don’t turn into cancer.

No medicine or vitamin prevents them or gets rid of them. Why they form is anyone’s guess.

A doctor can scrape them off with a spoon-shaped instrument called a curette or can freeze them off. If they aren’t irritated or irritating, or if they are not a cosmetic catastrophe, a person can choose to ignore them without any consequences to his or her health.

DEAR DR. DONOHUE: I would like to donate blood, but am timid about it. I have been known to faint around needles, even when one is used for only a second. I try to distract myself, but before I know it, I am on the floor. I know that sometimes good intentions are ill-advised. Would I cause more trouble than it’s worth? – N.N.

ANSWER: Your intentions are not more trouble than they or you are worth. Why not pay a visit to a blood donation center and sit and watch what goes on to desensitize yourself? It might take more than one visit. When you donate blood, you are lying down. Stay lying down for long after the needle has been removed, and during that time, listen to some music or an audiobook. Your generosity deserves recognition.

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.