Worse, if you work in a professional environment, it looks unprofessional and can be distracting to others.
If you are a chesty woman with a similar problem, it's easy to fix. Please do so.
There are several solutions:
- At a minimum, at least wear a shirt under it so that we don't have to see your bra. Or worse.
- Also a minimum requirement: wear a properly fitting bra. Get a professional fitting at least once a year because your body can and will change over time. There should be no obligation to buy. For instance, Nordstrom offers fittings for free.
- Get your shirts tailored. Yeah, I'll get on that as soon as I win the lottery. And as fate would have it, you'll still manage to move in a way that will make the shirt gap at least some of the time.
- Double-sided clothing tape placed on the fabric between the buttons (available even in your grocery store in the household aisle, near the sewing kits). It's also called "fashion tape." I recommend owning some for emergency use regardless.
- Use safety pins instead of fabric tape. Button up the shirt, turn it inside out, safety pin together the fabric between the buttons, then turn it right side out. You can only do this on shirts you can pull over your head, which is more possible than you think. Surprisingly, you can wash the shirt like this, and I recommend doing that. You can also pin the fabric while you are wearing it, but that is more difficult. Similarly, once you're comfortable with this, you could sew the gap shut as a more permanent fix.
- Sew a snap closure or two in the middle between the buttons. This will take some trial and error, or you might just make smaller gaps.
For more fashionable and/or tznius uses for fashion tape, see 1,001 Uses for Fashion Tape.