I’m guessing you’re looking for female problems because of where you posted the question.
Endometriosis isn’t taken seriously by many doctors. Mainly because they’re male, and can’t comprehend the extent of pain it causes to women. It’s frustrating to lots of women who are in terrible pain, because doctors can make them feel like their pain is all made up, or like they’re trying to get strong medication for recreational purposes. It’s the worst feeling ever - then when you finally find a doctor who listens to you and helps, you start to feel like maybe you weren’t crazy after all!

Well, a number of different cancers spring to mind. Skin cancer for one! I guess I’m not quite sure what you’re asking though. Are you asking for specific conditions, or for general health issues, like obesity and drugs and smoking… because drugs and smoking arent health conditions (illnesses), but health issues.

And I’m relatively curious as to why you’re asking.

gonneria syphilis hiv aids ppl dont take everything serious enough