Of allergy, intolerance, and sensitivity

"I'm allergic to that."

We've all heard someone say it.

But what does it mean?

If someone is "allergic" to something, it can mean anything from slight discomfort to death. Doctors and researchers add more precise meanings to "allergic."

ALLERGY = IgE

A "true" allergy is what doctors call a Type 1 IgE hypersensitivity. This is an immune overreaction to a foreign substance. It is immediate, but can take on any number of symptoms from hives, to congestion, to closing of the airways.

Yet, even in this "true" allergy area there is gray-- there are IgE-mediated, delayed hypersensitivities, as well. Even those these are "true" IgE responses, I have found that most doctors do not give them the same revered status as immediate IgE responses.

There are some other allergy categories, and for the sake of time, I'm going to move quickly. So, hold on!

Type 2-- Cytotoxic Responses-- these are the IgG and IgM antibody reactions, such as seen in some Autism food allergy panels, thrombocytopenia, and Goodpasture's Syndrome.

Type 3-- Immune Complex Disease-- this is also an IgG category. Lupus would fall in this category

Type 4-- Delayed hypersensitivity-- this is a T-cell mediated response, as in Multiple Sclerosis.

Type 5 (some scientists don't think this category exists)--Autoimmune disease-- Again an IgG and IgM response. Myasthenia Gravis and Graves' Diseases would be listed here.

Whew! All the allergy types.

INTOLERANCE = METABOLISM

An intolerance is when the body cannot absorb or metabolize a certain substance. It can be anything from gluten, to fructose, to various vitamins and minerals. It is usually a delayed reaction, in terms that it will not make sick the moment you eat it. This is usually because the problems happen in the intestines and the food isn't there yet.

The reasons for intolerance are as varied as the causes. An enzyme may be inadequate or missing, such as in lactose intolerance. A transporter may be lacking, as in fructose intolerance. Or the cause may be unknown.

And just to muddy the waters, some doctors put Type 2-5 allergies in this category, too. You know. Because they aren't TRUE allergies.

Symptoms can range from abdominal cramps, diarrhea, and constipation, to hay fever and coughing, to neurological disruptions.

SENSITIVITY = NORMAL, JUST BIG

A sensitivity is an exaggerated, normal side effect of exposure to a substance. Irregardless of the reason.

For example, 500mg of caffeine causes shakiness in most people. If 50mg of caffeine causes Bob to be shaky, then Bob is sensitive to caffeine. The shakiness is a normal response, just not at such a low level. Why is Bob shaky? I have no idea--it could be an intolerance--but it is still a sensitivity because caffeine will cause shakiness in most people at 500mg.

A sensitivity can be caused by an intolerance. This is why sensitivity and intolerance are often used interchangeably.



More Information:
Wikipedia: Allergy
Wikipedia: Hypersensitivity (Great description of Allergy Types)
Wikipedia: Food Intolerance
Caffiene Tremors
Milestones: What is the difference between allergy, sensitivity, and intolerance?