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Allergies and Poison Ivy Treatment
By Lou Paun

We all know about the horrible itchy rash that poison ivy causes. It is formally called “allergic contact dermatitis”.

Dermatitis is an inflammation of the skin; in this case, it is caused by something that came in contact with the skin, so it is a contact dermatitis. Many other things — soaps, perfumes, clothing — can cause contact dermatitis if the person who touches them is allergic to the item.

An allergy is a response by the immune system to a foreign substance in the body. Usually, that’s a good thing; it’s our immune system that fights off germs and keeps us from catching diseases. Sometimes, though, the immune system attacks a foreign substance that is really harmless, and ends up causing an inflammation. This is what happens when people touch poison ivy.

The inflammation is created through a sequence called delayed hypersensitivity. The sequence begins as soon as a person touches poison ivy, but the results are not noticeable until later. Sometimes the inflammation appears after a few hours, but it can be delayed for a full day. This is quite different from the irritation caused by plants like nettle and euphorbias, which show an immediate effect.

The culprit is urushiol (pronounced oo-roo-she-ol), which is found in all parts of the plant except the pollen. Animals rarely have a reaction. Birds and bears eat the berries, and cattle, deer, hogs, and goats graze on the leaves and stems.

Most humans, however, have a strong allergic response to urushiol. According to the Food and Drug Administration, 50% of people are allergic to poison ivy the first time they come in contact with it. About 90% of the population will become allergic after repeated exposure. We’ve all known people who boast of being immune to poison ivy, but most of them suddenly develop a response if they touch it repeatedly.

People have different levels of sensitivity to urushiol. Some people have only a mild allergic response. Most people will get a rash if they are exposed to 50 micrograms of purified urushiol. That’s a tiny amount. For comparison, remember that one grain of table salt weighs about 60 micrograms. Highly sensitive people react to even tinier amounts. About 20% of the population react to the presence of as little 2 migrograms of urushiol.

Urushiol is concentrated in the sticky sap of poison ivy, a plant characterized by plentiful resinous canals. If it isn’t washed off right away, the urushiol is absorbed through the surface of the skin and binds to inner-skin proteins to create new compounds. Once it has reached that point, it can’t be scrubbed off.

What happens is this: urushiol penetrates the stratified squamous epithelial cells of the skin. Then it binds to large dendritic (branched) white blood cells in the epidermis called Langerhan’s cells. A Langerhan’s cell, with urushiol bound on its membrane, migrates to a nearby lymph node. There, specialized white blood cells called effector T-cells recognize the presence of urushiol. Effector T-cells, sometimes called “helper T-cells”, patrol throughout the blood and lymphatic system, each carrying special receptor molecules on their membrane that will identify a specific intruder. They’re like the world’s most efficient security guards.

When the effector T-cell recognizes urushiol found to a Langerhan’s cell, it attaches to the cell. It releases special proteins to attract several different kinds of white blood cells. These include “killer” cytotoxic T-cells and “cell engulfing” macrophages. This army of white blood cells attack the urushiol-contaminated Langerhan’s cell, and release lytic enzymes and protein toxins that destroy everything in the vicinity. They destroy the membrane-bound urushiol, but they also destroy many other skin cells. The blistering, itchy rash we call “poison ivy” is the noticeable result.

Lou Paun blogs about poison ivy (she hates the stuff!) and poison ivy treatment at http://poisonivytreatment.blogspot.com

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