Zip-lining is among the high-risk activities that are not covered by travel insurance. (iStock)

If you think your travel insurance policy will protect your upcoming summer vacation, you might want to take another look. Travel insurance doesn’t cover everything. Truth be told, it might not cover anything.

The list of exclusions is long and includes everything from pregnancy to scuba diving. When you buy travel insurance, it’s important to make sure you understand what it does — and doesn’t — cover. Don’t wait until the last minute to review your policy. By then, it may be too late.

Consider what happened to Jen Coburn recently when she booked a flight from San Diego to New York on American Airlines. At the end of the transaction, the airline made a high-pressure pitch for travel insurance: She was asked to choose between “protecting” her trip with insurance or leaving her trip “unprotected.”

“I knew my plans might change, so I bought the insurance,” says Coburn, a book publicist from San Diego.

Later, when she canceled her plans, she discovered that she wasn’t covered by the insurance. “They said that I was only covered for a ludicrously few extreme circumstances. The most laughable one was if the airline canceled my flight,” she says. “Yeah, if the airline cancels the flight, I definitely get my money back without the stupid insurance.”

Airlines that sell travel insurance disclose the terms online, but they’re easy to ignore. The coverage was in the fine print,” Coburn concedes, “but I felt duped.”

Part of the problem, says Michael McCloskey, an associate professor at Temple University’s business school, is that consumers don’t understand how insurance works. Most travel insurance, he says, is the “named perils” variety, which is to say it covers only what’s named in the policy.

But travel insurance companies often oversell the benefits when they promote their policies, promising that insurance will “protect” your vacation. In fact, travel insurance only protects what the fine print says it protects. Among the most notable exclusions:

Preexisting medical conditions: This is perhaps the biggest gotcha when it comes to exclusions. If you have a medical condition before you buy a policy, and it flares up before or during your trip, your policy may be worthless. Some insurance companies offer a waiver of the preexisting condition exclusion, but only if you buy trip insurance within a specified number of days from the date you pay your initial trip deposit. However, more insurance companies are now offering coverage for preexisting conditions, says PK Rao, president of INF Visitor Care, a travel insurance firm. "As preexisting conditions like high blood pressure and diabetes become more prevalent, there's more demand for coverage," he says.

Pregnancy: Childbirth typically isn't covered as a travel insurance medical benefit. Some travel insurance companies offer plans that cover pregnancy-related complications, but they're limited to 26 weeks' gestation and have lower dollar amounts than typical medical-emergency coverage. The bottom line is, if you're traveling while pregnant, don't count on traditional travel insurance to pay for pregnancy-related medical care.

Mental illness: Mental illness is not typically included in travel policies. That includes canceling your flight because you're afraid of flying or you're anxious about your safety at your destination; most travel insurance companies summarily dismiss those claims. The fix is to buy "cancel for any reason" coverage. "A trip can be canceled and policy paid out should a traveler fall into depression or need to tend to their anxiety," says Maxime Croll, Maxime Croll, who heads up the insurance research division at ValuePenguin.com, a consumer finance website.

High-risk activities: Most travel insurance doesn't cover high-risk activities such as scuba diving, bungee jumping or even zip-lining. Sheryl Hill, the executive director of Depart Smart, a nonprofit group that promotes travel safety, remembers the case of a traveler who was injured while zip-lining in Mexico. "He awoke in a hospital in a leg cast with purple toes," she says. His travel insurance wouldn't pay for medical evacuation because zip-lining wasn't covered, so he booked a commercial flight back to the United States, delaying his treatment. Doctors could not save his leg.

There’s so much more that traditional travel insurance policies don’t cover that it wouldn’t fit in a single column. But there’s one workaround.

“You can buy ‘cancel-for-any-reason’ coverage, which does exactly what it says,” says Steve Pritchard, the founder of Cuuver.com, an insurance comparison site. “This extra coverage can be extremely helpful in protecting you from having to cancel due to unforeseen circumstances. It also gives you the flexibility to cancel your trip should you realize that the trip is no longer to your tastes or is no longer feasible financially.”

Bear in mind, though, that a cancel-for-any-reason policy is more expensive and comes with significant restrictions. This type of policy can set you back about 10 percent of your trip’s prepaid, nonrefundable cost, compared with 4 to 8 percent for a named-perils policy. And with a cancel-for-any-reason policy, you don’t get a full refund, but from 50 to 75 percent of the cost of your trip.

All of which brings us to the biggest mistake travelers make when they buy insurance. They get the timing wrong. The time to think about insurance is before you book your vacation. You usually have from one to two weeks after booking your vacation to buy insurance.

You also need to read the policy before you buy it, not when you sit down to file a claim. Most travel insurance companies offer a “free look” period of up to two weeks: Change your mind about the policy, and you can get a full refund.

If you read the fine print, you can avoid some of the gotchas. Otherwise, you could discover that your policy is worthless.