You are in control.

Stroke—which occurs when a blood vessel that supplies blood to the brain becomes blocked, or a blood vessel in the brain bursts—has a scary reputation. And for good reason: Stroke is the no. 5 killer of Americans and a leading cause of disability. But you are not powerless against stroke. Doctors weigh in on what you need to know about stroke and how to take control.

1. Know the symptoms.

First things first: When talking about stroke, every doctor stresses the importance of recognizing the signs of stroke and acting on them. Try this test: If you think someone is having a stroke, ask him to smile. Does one side of the face droop? Have him raise both arms. Does one drift downward? Give him a simple phrase to repeat. Is his speech slurred or strange? If you notice any of these signs, don’t delay— call 911.

2. “It can happen to anyone.”

Think stroke is only an older person’s disease? Although the risk of stroke increases with age, anyone—even infants and children—can experience a stroke. “Many people dismiss symptoms because they think they’re too young for a stroke,” explains Rani Whitfield, MD, family medicine physician. “But the truth is, you’re not. Be prepared and seek help immediately if you suspect one.”

3. “Waiting is the worst thing to do.”

When you delay seeking treatment, more brain cells die. “Some people dismiss symptoms like numbness in the arm or slurred speech to being tired or sleeping in a funny position,” says Grahame Gould, MD, vascular neurosurgeon. “Even if you’re not sure it’s a stroke, call 911. I’d rather patients come in and be wrong than wait to make sure. By then, it may be too late.”

4. “Step in to help someone else.”

See a friend or family member acting strangely? Think it could be signs of a stroke? Take action. “Because stroke affects the brain, it can rob people of the ability to recognize that anything is wrong. This is true even if a person is experiencing a major stroke,” says Dr. Gould. “Usually, it’s up to others—not the stroke victim—to get help.”