Sure sounds like she is bi-polar.

You are not your SIL's babysitter. Nothing you say or do will change her so just stay out of it. If Mom has a problem with her, your husband has a problem with her, they need to do their own dirty work. Tell them to voice their concerns to a professional. Sick or not, SIL is a grown woman and she can live how she pleases. No one may like it but it's her choice.

She needs to get a dosage adjustment, or change meds. Psychiatrist ASAP! This is judgement impairment and she could her safety in jeopardy.

It's not your place. Say nothing. She's under care.

I agree with the above, that it's not the tattoos that should be of concern. If she's bipolar, is she in a manic phase? You said she's on medication, but does she see a therapist and/or a psychiatrist regularly? Her medical professional needs to know what she's been doing the past year so he/she can assess whether she needs her medications adjusted, lest this (maybe) manic phase spin seriously out of control.

How old is she? If she's young, is it possible she's just looking for a different direction in life? Maybe this ultimately isn't a big deal.

BUT being bipolar, this behavior does seem alarming. I would definitely express concern to her, and try to get your MIL to back off, because I don't think she's seeing the bigger issue.

Don't say anything about the tattoos. Don't make it about the tattoos. But do check in on her and help her have perspective.

I wouldn't touch that with a 10 food pole.

I would not mention the tattoos but I think it's a good idea to check in with her, let her know you care and are there if she needs something.

If I were you, I would do nothing.

If I were your MIL, I would not focus on the most benign thing, the tattoos.

If I were your husband (if I've got the relationship right), I'd ask my sister if she were ok and if there's anything I can do to help.

My SIL has some tattoos. A year ago, she only had one medium tattoo on her lower back and a medium tattoo on the back of her calf. In the past year, she has made a lot of impulsive life decisions; quitting her well-paying job because she was unhappy, jumping from serious relationship to serious relationship with guys she did not know very well, trying to move abroad and moving to another city. In addition to these things, she has made a lot of changes to her physical appearance - dying her hair various bright colors, piercing her nose, and now she has suddenly drastically increased her tattoos. She has added about 3 large tattoos to her back, so her whole lower back is covered. She got her entire calf tattooed and is planning on getting the other tattooed in a week.

I don't have any tattoos but personally I don't really care about those that do. However, given my SIL's erratic year and emotional instability, I am concerned about her and wish she would slow down a bit. She is bipolar and already on medication and seeing someone. My MIL and husband are upset that she is getting more and more tattoos, especially in such a short time span. I know my SIL knows how they feel, but she does what she wants anyway. My MIL is so distraught about the tattoos that she has begged me to say something to my SIL. She thinks that maybe my SIL will listen to me. While we do have a good relationship, I don't think she would really listen to me, even though I am concerned about it in the context of everything else she has done. I also would not want to come off as telling her what to do, particularly as I am a couple years younger than she is. Given these circumstances, WWYD? Express concern, or say nothing?