Malaria is an infection that’s carried by some mosquitoes, especially in hot, tropical places. It can make people very sick, and many have died from it.

Sickle cell trait is a blood condition that runs in some families. People with it have one copy of the "sickle cell gene," but they don't have sickle cell disease.

If a mosquito carrying the malaria germ bites someone with sickle cell trait, the person isn't as likely to get as sick as other people. That’s because people with sickle cell trait have red blood cells that make it hard for the malaria germ to grow.

Scientists believe that sickle cell trait happened thousands of years ago when a person was born with a random small change in one of their genes. Genes are the instructions for lots of things, like our eye color, height, and how our body works. That changed gene turned out to be sickle cell trait.

People who were born with sickle cell trait were better able to survive malaria and pass on the changed gene to their children, who passed it on to their children.

Today, people with sickle cell trait have it because it was helpful to their ancestors a long time ago.

If you have sickle trait and plan to travel to a tropical area with malaria, you still need to protect yourself. Ask your doctor what you need to do to avoid getting sick.