My bmi seems really low is that a bad thing?

It can be: For a 20 year old female, your BMI should be at least 20. Too much lower risks causing negative effects to hormone metabolism, bone growth, and immunity.

Depends on your body: People come in all shapes and sizes. BMI is a useful ratio for the majority. People on either extremes of normal may have a high BMI (think bodybuilder) or low BMI. Either ends of the spectrum may be healthy, so it really depends on your individual body. Talk to your physician for specifics about you.

Put on a few pounds: Hi Jerry, The weight recommendations, such as the BMI, are designed to be guidelines for healthy weight. Being significantly below the guidelines would suggest that you are at risk in ways that people in the normal range are not. If you could get your weight into the lower normal range of BMI that would likely improve your health. Be sure to discuss this with your primary doctor - soon:)

BMI: Hi, If your BMI is less than 20 then it's concerning and you need to find out why, anything above that and below 25 is fine.