Does not being a part of NHS hurt your chances to schools? A lot of kids in my school do it.
Some of my classmates said it is a red flag if you are not in it, is this true?
Thanks
Personally I don’t think so. I believe that following your passion is something much more meaningful than NHS. Do something that sets you apart. Good luck! 
I would not suggest using 16-17 yo’s who have no idea how much they do not know as a primary source in info on this subject.
No, it will not matter. While the volunteer opportunities that can happen with some NHS chapters are helpful, one can pursue opportunities outside of NHS. Simply being in NHS is about as meaningful to college admissions as a perfect attendance certificate, IMO.
Being an officer in NHS might make a difference, but not all member get an office… Being in NHS can be an indication that the school acknowledges what you have done to qualify, but the same can be shown through the various portions of your application. NHS might be make or break for someone who isn’t involved in any other ECs, because their focus is only on studying.
To me, NHS is public acknowledgement of your grades and community service. If you have the grades and you have the community service, then you are good because that is what colleges want to see. The NHS is just a cherry on that sundae. Also, NHS is a public celebration of all your hard work…one that your parents will very much appreciate.
So if your question is: I was not invited to apply, then it has no bearing…it will be all about your grades/Service.
If you were invited to apply, and want to know if you should bother, then I say do it for your parents. They will be so proud.
-A Parent