Why arent all
people sensitive?
People vary in their sensitivity
to poison-oak just like they vary in height and weight.
Why arent
animals sensitive?
Actually, there are two answers
to that question. One answer is that different species vary in
their sensitivity, just like people differ from each other.
Goats are specialized to eat terrible stuff; they relish
poison-oak, but they also ate the tarpaper on my fathers
chicken coops! Pack rats use poison-oak as a defense against
other animals; they build nests out of the stems. Deer
sometimes eat a few branch tips in late winter, but horses
ignore the plant. Guinea pigs eat it if they have nothing else
to eat; but then they vomit blood, convulse and die.
The other answer is hair. For
example, guinea pigs seldom react to urushiol painted on their
skin; but shave and lightly sandpaper them and they react
exactly like people do. And, people get rashes worst where
they have the least hair.