You can order a pizza, a latte, movie tickets or your next car online, so why is it so darned hard to email your doc?

According to a new report, doctor-patient emails can help keep major health conditions like diabetes and high blood pressure under control with fewer trips to the physician’s office.

A whopping 93 percent of Americans want to email their health care providers. But while 75 percent of American doctors use electronic medical records, surveys show that only about 20 percent communicate electronically with their patients.

Getting in the way are serious challenges such as complex computer systems, a lack of payments to docs for their email time and docs’ fears that their inboxes will be overloaded with messages.

Those issues need to be resolved. But in the meantime, there is something you can do. Surveys also reveal that plenty of people don’t take advantage of secure messaging services when medical practices do offer them.

In a recent Harris Poll, 64 percent of Americans admitted that they don’t use online “patient portals” that give them access to test results, easy prescription refills and, for some, email. One in three didn’t even know they existed. Still others try to reach out to their doc the wrong way with personal questions, such as on social media.

Emailing your doc has its own set of rules. Hint: Don’t send that cat video from Aunt Martha.

Here’s what to know about making the most of it:

Keep it short. Use email to ask brief questions, not to get a diagnosis for a new problem or for treatment advice for new symptoms. Unlike lawyers, your doc isn’t paid to do this. Ask simple questions with yes or no answers. For other questions, schedule an appointment. Resist the temptation to reach out just to chat or pass along jokes, baby pictures or cat videos. (Our families send us plenty of those already!)

Don’t ask your doc to practice social-media medicine. When Johns Hopkins Bloomberg School of Public Health polled 2,252 healthy adults recently about how they communicate with their doc, a startling 20 percent said they’d tried to make contact via Facebook. It’s fine to “like” your doc’s office on Facebook, after all, more and more have a presence and may even post useful, general health info there. But don’t expect a conversation about your symptoms. Social media’s just too public.

Do use the portal. To keep email exchanges and access to your electronic health records private and secure, more and more health care practitioners are setting up password-protected patient portals. But often, people ignore them; in one recent study of more than 100,000 people, just one in four signed up. In another, just 7 percent used portals on doctors’ websites to track their health or fill a prescription.

We know. Signing up means one more username and password to remember, and one more website to figure out. In one European survey, 11 percent of people who didn’t use their doc’s portal said a lack of computer or Internet savvy got in the way. If that’s you, ask a friend or family member to help you get started. Your doc’s portal is the best way to check text results, order prescription refills, even request referrals and if your doc’s tech-savvy, to leave an email he’ll return.

Think twice about including extremely sensitive or embarrassing details. Remember that email to your doc may be read first by a nurse or office assistant.

Ask about response time. This isn’t Snapchat. Many docs and medical offices try to answer emails within 24 to 48 hours. Call or find out at your next visit what your provider’s policy is for response time.

Don’t use email for emergencies. In a lot of pain? Got a scary new symptom? Call your doctor or call 9-1-1, especially if you think that you or a loved one may be having a heart attack or stroke or other medical emergency.

Mehmet Oz, M.D. is host of “The Dr. Oz Show,” and Mike Roizen, M.D. is Chief Wellness Officer and Chair of Wellness Institute at Cleveland Clinic. To live your healthiest, tune into “The Dr. Oz Show” or visit www.sharecare.com.