There are several factors that can disqualify you from military service, including medical conditions, criminal history, age, physical fitness, and drug abuse. Here are some examples of disqualifying medical conditions:

• Blood and blood-forming tissue diseases, such as anemia, hemorrhagic disorders, leukopenia, and immunodeficiency.
• Diseases of the jaw or associated tissues that are not easily remediable, and will incapacitate the individual or otherwise prevent the satisfactory performance of duty.
• Arthritis, chronic osteoarthritis or traumatic arthritis of isolated joints of more than a minimal degree, which has interfered with the following of a physically active vocation in civilian life or that prevents the satisfactory performance of military duty.
• Allergies resulting in systemic symptoms, such as food allergies.
• Un-united fractures, history of instability of a major joint, certain retained orthopedic fixation devices, severe scoliosis, or any condition that could interfere with daily participation in rigorous physical training or athletic programs, wearing of military equipment, or detract from military bearing and appearance.

In addition to medical conditions, criminal history can also disqualify you from joining the military. For example, if you have a history of certain violent offenses like statutory rape or aggravated assault, you won’t be allowed to enlist in any military branch. Other disqualifying factors include failing to meet minimum educational requirements, having a dishonorable discharge from the military, or having a record of mental illness.