No one really knows what causes lupus, but it isn’t contagious, which means you can’t catch it from someone who has it.
Scientists think that some people may be more likely to get it because of things they can’t control like:

 being a girl [girls and women get lupus more often than boys and men]

being a certain race [African-, Asian-, Latin- and Native American people are more likely to get lupus than white people]

having a gene or genes that makes you more likely to get lupus [about 10% of people
with lupus have a family member with the disease]

Sometimes intense stress or infection can be the trigger, but neither one actually causes the illness.
But if a person’s genes make him or her more likely to get lupus, extreme stress or an infection may cause the disease to first show up.