Is being 5'6 and 110 lbs. unhealthy?

Likely you'll full out as you get older. If you eat a bunch you're probably fine. If you're worried ask a doctor, not an internet forum that doesn't even make you register.

Run Doctor wrote:

For a female athlete it is healthy

No, a female runner should be more like 95-100 lbs. at that height. For a male it is nearly perfect. Ritz was 115-120 lbs. and he is 5'8", so you are golden.

For all of high school I was 5'10" and between 120 and 125 lbs. I couldn't gain weight. Somehow, I got to college, bumped mileage, and now weigh in about 130-135 after 4 years of consistent weigh ins. Some people are naturally thin, running doesn't help. But your body peaks and plateaus, and everybody develops differently. I wouldn't worry about it too much, it's just numbers.

*guy underweight, girl fit. Ftfy

That what I weighed in the 4th grade.

Pics?

If your BMI is under 25 and your eating habits are healthy, then you’re good. Most people should be worried about how they eat way too much.

My wife is 5'1", 105 pounds and wears double 00 (XXS) pants which means a 22" waist. People tell her she is too skinny. She doesn't have boney arms or legs. ...

If your height and weight are real, then you are ultra-skinny and have boney arms and legs, which makes you look anorexic even if you are not.

if you're fueled and content than you're fine. All bodies are different. You may have lighter bones and muscles mass. My 16 year old son is taller but thin build as well. He eats good enough for a teenager (not the healthiest of eaters) but he's fueled. He'd live on dr. pepper if I let him. He's a runner as well. I wouldn't worry about it...you will start to grow and gain weight and muscle naturally. His Dr. said because he's growing and running high mileage he recommends a multi vitamin but other than that he said he's growing and healthy following his growth through childhood. He also takes vitamin D, especially this time of year when its gloomier and darker. I also recommend a post run protein drink of something. We like Amino VITALS Rapid Recovery Post run with BCAA's Amino Acid. You can get it on amazon.

If you are female - no.

If you are male - yes. Emaciated is more like it.

5'6 and 110 is unusual but not necessarily unhealthy, depending on what you eat, etc. I was 6'0 and 110 as a HS senior and skinny but healthy, with no eating issues (though it probably wasn't a good idea to eat a half-gallon of ice cream for desert every night). Several decades later, I'm 6'0 and 135 after cutting out most deserts.