dentist
A dentist is a person who specialises in the mouth and treats diseases and problems of the teeth.
depression
Depression is a disease that causes you to have negative emotions, feel joyless and sad.
dermatologist
A dermatologist is a doctor who specialises in the skin.
diabetes
Diabetes is a disease that causes you to have too much sugar in your blood, making you very thirsty and as a consequence having to pee a lot.
diarrhoea
Diarrhoea is referred to flimsy, even liquid poop that causes a tummy ache.