Houston, Texas (NAPSI) - It happens all the time: You’ve been swimming a lot and then one night when your head hits the pillow you suddenly notice that your ear hurts. You’ve got swimmer’s ear but what causes it? Surprisingly, swimmer’s ear is not caused by swimming at all.

It’s simply associated with swimming. It’s actually caused by bacteria or fungi that invade the ear canal.

Understanding the details behind this sort of thing is what the scientists known as toxicologists routinely do—that is, they determine the difference between what might cause an adverse health effect and what might only be associated with it.

Understanding causation versus association can be difficult, especially when it comes to health and the possible factors in producing or preventing a disease.

For example, people used to believe that stomach ulcers were caused by stress and spicy food. It’s now known that ulcers are caused by the bacteria H. pylori. There was an association among ulcers, stress and spicy food, in that they often occurred simultaneously, but stress and spicy food don’t cause ulcers, bacteria do.

Causality, toxicologists say, can be proven only by demonstrating how something actually leads to an effect. The challenge in cases of such conditions as Alzheimer’s, ALS, MS, autism, ADHD or Parkinson’s disease is that it’s extremely difficult to know if a toxin or some other factor is involved with the disease. Certainly, no one would suggest giving a known or even potentially toxic substance to people on purpose, so most such medical research can only indicate correlations. That means any potential role of environmental or dietary factors in human disease must be done through studies that investigate the common factors among people (diet, habits, workplace) that could provide a connection to the disease. These epidemiology studies are still limited in that they can only reveal potential associations and can never prove causation.

Even when scientists warn there’s more work needed to prove causation, many people leap to thinking they should eat or not eat a specific food or take a specific nutritional supplement. One hears “eating fish prevents heart disease” when in fact the research found only that heart disease is less frequent among persons consuming fish—an association but not necessarily a cause—and fish eaters do still get heart disease.

That’s why, when new research comes out on potential associations between agents or activities and disease, everyone should carefully weigh the information before making any lifestyle changes.

You can learn more from the experts at the Society of Toxicology at and (703) 438-3115.