DEAR DR. DONOHUE: I own a lawn service, and every year I catch poison ivy. Would you answer some questions my crew and I have? Can a person give it to another? What part of the plant gives it to you? What does poison ivy look like? What’s the best treatment? – W.N.

ANSWER: The sap of the poison-ivy plant (or poison oak or poison sumac) is the stuff that causes poison-ivy rash. It comes from the leaves, stem or roots of the plant if they are broken and are leaking sap.

The first contact with sap doesn’t cause an outbreak, but it sensitizes a person. Upon the next exposure, he or she will break out in a rash one to two days (the range is six hours to 12 days) after getting sap on the skin. At first, the rash is nothing more than itchy, red lines, but soon blisters appear. The rash lasts about three weeks.

Blister fluid does not spread the rash to others, so poison ivy is not spread from person to person. Only sap spreads it. The sap can cling to clothing, pets and tools, so contact with sap-covered objects can spread the rash.

The poison-ivy plant has oak-leaf-like, green leaves in clusters of three. That’s a poor description. The best way to familiarize yourself with how it looks is to get hold of a picture of it. You can find one in your local library. Furthermore, the plant’s appearance varies in different locations. You can test a suspect plant by first putting on vinyl gloves and then putting the end of a leaf stalk on white paper. Crush the stalk with a stone to release sap. If the plaint is poison ivy, the sap will turn brown in about 10 minutes.

Washing as soon as possible after exposure can prevent the rash, but you have to act fast — 15 to 30 minutes is all the leeway you have. Barrier creams like IvyBlock or Stokogard Outdoor provide some protection.

Cool compresses saturated with plain water or Burow’s solution relieve the itch, as do lotions like calamine lotion. When the rash is not localized to one or two spots, tepid baths with colloidal oatmeal or cornstarch stop itchiness. Cortisone skin creams and lotions also work. In extensive and serious outbreaks, oral cortisone is prescribed.

DEAR DR. DONOHUE: I am pleading for information on osteomyelitis. Our great-grandson has it. He is 5. All I read about it – and this is not much – indicates it is very serious. – C.S.

ANSWER: Osteomyelitis is a bacterial infection of bone. It is serious, but it is treatable and, in most instances, curable.

Bacteria can invade bone from a nearby infection, like an abscess. Or if the skin is cut and bone juts through it, bacteria can directly infect the exposed bone. Such happens in fractures where the broken ends of bone protrude through the skin.

In children, and sometimes in adults, bacteria are carried to bone in the blood. Bacterial invasion of the blood is a common daily occurrence. Most of the time, it’s a transient affair, and the body disposes of the bacteria without trouble. In a few exceptions, the bacteria take up permanent residence – in the bone, for example – and they begin to multiply in that site.

In children, once antibiotics are started, improvement is often rapid. If there are fragments of dead bone in the infection site, the doctor has to remove them before the antibiotics can take hold.

Not all osteomyelitis infections are as straightforward and easily controlled as I describe. Some require prolonged intravenous antibiotic therapy, and often that must be done in the hospital.

DEAR DR. DONOHUE: My grandfather died of a pulmonary embolus at 56, and my mother suddenly died last month at 64 from one. I was hospitalized for a possible pulmonary embolus. Should I let the doctor know my mother and grandfather died from one? – T.C.

ANSWER: Definitely and quickly. A pulmonary embolus is a blood clot in the lung that often comes from a clot in one of the leg veins. Families with a history like yours can have a clotting disorder that makes them susceptible to clot formation. You should be checked for these conditions.

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.