Here’s something you need to be aware of when seeking insurance quotes: almost every insurance policy has at least one or more exclusion. So what is an exclusion?

An exclusion is a provision in an insurance policy where your insurance coverage is not valid if certain things happen. Here’s a common example: your personal auto insurance policy most likely would not pay for damages if you had an accident while using the car for business purposes, because of the commercial operations exclusion.

Here are some other common insurance exclusions you may not be aware of:

Your home insurance almost certainly does not cover you if your house is destroyed by enemy bombers during a war. However, while home damage from acts of war is not covered by insurance, damage caused by acts of terrorism typically are covered. In that case, it may come down to whether the government defines the incident as war or terrorism.

If your home is flooded, your claim will be denied unless you purchase special flood insurance. And nuclear accidents are normally not covered, so keep that hopefully remote possibility in mind if you’re buying a home near a nuclear power plant.

In a down economy, insurance companies look for ways to cut costs just like everyone else, and one way to do that is to add more exceptions to your insurance coverage. The typical health insurance policy may be full of exceptions that you don’t know about until you file a claim. For instance, home care and home nursing are usually not covered.

While vasectomies are covered, vasectomy reversals are not. Unconventional treatments or drugs considered to be experimental will not be covered. And if you decide to get a sex change operation, you will have to pay for it yourself.

Sometimes, when policy holders and insurance companies interpret an exclusion differently, a lawsuit is the result. In 2009, a Louisiana homeowner with an “all-risks” policy sued his insurance company for denying a claim he filed after sulfuric gases from tainted Chinese drywall in his home corroded some of the house’s wiring.

The company, based out or Baton Rouge, Louisiana, argued that the damage from the drywall was not covered because of the policy’s pollution exclusion. However, a judge ruled that the pollution exclusion was not intended to apply to damage from inferior building materials, and ruled in favor of the homeowner.

Exclusions in coverage are a very common thing in policies, so be sure you know which exclusions are in place when you’re shopping for insurance quotes. If your quote seems low, it may because there are a lot of exclusions in the policy. You’ll definitely want to know what those are before purchasing.