It is not always possible to avoid petechiae. Avoiding trauma will help prevent petechiae caused by injury. If allergy to a medication is the cause, avoiding the medication will help prevent the condition. Prompt treatment of infections will help prevent sepsis.
The long-term effects of petechiae depend on the cause. For example, petechiae caused by injury will usually fade in time, and cause no long-term effects. When the cause is allergy to a medication, stopping the medication should end the condition. A person who has a severe infection with petechiae may be very ill, and death can occur.
Most cases of petechiae are not contagious and pose no risk to others. If the cause of petechiae is an infection, such as mononucleosis or meningitis, the infection may be contagious.