A number of health conditions can disqualify someone from joining the military, including:
Skin conditions
Eczema, atopic dermatitis, psoriasis, and severe acne can disqualify someone.
10% of adults have eczema
Respiratory conditions
A history of recurrent bronchospasm, such as from asthma, can disqualify someone.
8.9% of adults have asthma
They are not allowed in the Military as well as some flat footed people
a person can be discharged from the military for sleepwalking.....the percent of people that sleepwalk is about the same as percent that is Trans
1.6% of the US population identifies as transgender.