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The Scenario:
It was blueberry season in Maine. The hillsides along the ocean were covered with low bushes of green leaves and midnight-blue berries, sweet and delicious. Raking the bushes to remove the berries was a living for many Mainers. For Susan, the thoughts of a freshly baked blueberry pie, and blueberry pancakes for breakfast, were all she needed to spend the morning hunched over under the hot summer sun.
Not being from the area, Susan was not familiar with all the local plants. Towards the edge of the field she got into an area where the berries were partially covered by plants with bright green shiny leaves set in characteristic clusters of three. She didn't recognize it as poison ivy, simply brushing the leaves out of her way. It was hot, and there were pesky mosquitoes biting her. Between swatting them, wiping the sweat off of her brow, and picking the berries, she had quite a busy morning.
After returning home she showered and got to work baking. Two days later the first signs of poison ivy began to break out on her hands and legs. Soon even her face and arms were involved even though she did not recall the leaves ever touching these areas. A week of misery began.
Questions:
Answer:
"Ouch!" Or is it, "Itch!" How about "Uh, oh"? Anyway you cut it, Susan is going to have quite a time of it.
Poison ivy is a type of contact dermatitis. Dermatitis means literally inflammation of the skin. And contact means that direct physical contact with an offending substance causes the dermatitis. With contact dermatitis, the rash is caused either by a chemical irritation of the skin, or as in this case, by an immunologic reaction to plant chemicals. As it turns out, the reaction to poison ivy is mediated by T cells -- the same group of immune cells that are affected by HIV. An oily resin from the leaves, stems, or roots of poison ivy called urushiol will cause a rash when brushed onto the skin. Even smoke from burning plants can carry the oil to the eyes, skin, and throat. But that's another story.
Poison ivy spreads if and when the oil is transferred from one part of the body to another. Swatting mosquitoes and wiping the brow will certainly cause spreading once the hands have touched the leaves. However, once you have bathed, using soap to remove any traces of the oil, no further spread will occur. The rash may appear to evolve over time. But that is not because it continues to spread. Rather, the rash evolves according to how heavily different parts of the body were exposed, and the sensitivity of the skin in that area. Likewise, you cannot transfer the rash to another person once the oil has been washed off. Fluid from the blisters will not spread or transfer the rash.
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