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The Historical Perspective of allergies.
Adverse reactions to wasp stings and certain foods were among the first allergies reported.
In the fourth century B.C. the Greek physician Hippocrates observed that milk made some people sick to their stomachs and gave them red skin weals. 
A few other foods — such as shellfish and nuts — seemed to cause similar symptoms, and occasionally made people go into shock.
Another Greek physician, Galen, noted that some plants, such as poison ivy, caused skin reactions in certain individuals.
Hippocrates and other early medical men tried to explain these unpredictable responses in terms of toxins that somehow harmed just a few people.
Several centuries later, the Roman philosopher Lucretius, in his scientific poem “De Rerum Natura,” observed:
“What is food to some may be bitter poison to others”
— or, as the saying, now goes, “One man’s meat is another man’s poison.”
In the sixteenth century, the Italian physician Leonardo Botallo remarked on a patient who got headaches and began to sneeze on smelling roses; another Italian physician reported someone who became ill whenever a cat was in the room.
An Italian astrologer cured an archbishop’s asthma by removing his featherbed and feather pillows. In the mid-1800s, the condition we now call hay fever was traced to grass and weed pollens.
Later, scientists showed that tiny amounts of pollen from specific plants could bring on nasal stuffiness, sneezing and eye irritation. The condition was worst during the pollination season, when pollen counts were high.
In the late 1800s, a German dermatologist, Josef Jodassohn, invented the “patch test” to show which substances, if put on the skin, would trigger itchy, red patches, revealing themselves as allergy provokers.
He also showed that dust mites — tiny sightless creatures, distantly related to spiders, that live in dust — would often cause an allergic rash and nasal stuffiness.
Why is shock serious?
The medical term “shock” refers to inadequate circulation of blood to the body’s tissues.
Shock can be caused by a loss of blood (hemorrhagic shock from severe bleeding), by a severe infection (septic shock) or by numerous other factors. Allergic shock is caused when the blood vessels become “leaky” and dilate (widen) so that the pressure of circulating blood (“blood pressure”) drops.
Since blood carries oxygen and essential nutrients to the cells of the body, a drop in blood pressure can disrupt the body’s functions. A person “in shock” will tend to be pale and cool, and may be dizzy or may pass out. If shock is not treated, it can cause death.
The word “allergy,” which comes from the Greek allos or “other” and ergon or “work,” was coined in 1906 by the Viennese pediatrician Clemens von Pirquet.
The term captures an essential aspect of allergy — namely, that it “alters” the “work” (reaction) in an allergic person’s body.
In 1910 Sir Henry Dale, a British scientist, identified histamine — a substance released by our body tissues, but first isolated from fungi, rye and other plants — as a key “mediator” in the body’s allergic response.
He showed that histamine acts to make smooth muscles contract, thus narrowing the breathing passages, and to make blood vessels dilate, thus lowering the pressure of the blood, also causing inflammation and purities (itching).
This explained some aspects of the allergic reaction: the hives, itching, swelling and in worse cases the breathing problems due to congested airways. Once histamine was identified as a key agent responsible for some allergic symptoms, the search began for antidotes — forerunners of today’s widely used antihistamines