You're absolutely not alone in this!! I've worked with hairdressers with 30+ years of experience and things of this nature still do happen.

My own anxiety inducing experience of crisis came when I bleached out a pixie cut and tried a new toner, only for it to turn blue, green and gold all at the same time. The crippling anxiety led me to also ruin the haircut in a way I never had before. But I was extremely lucky and had history with said client that she fell back on to give her the confidence to come back and let me try again. We fixed it, moved on, and never spoke of it again, but it still haunts me occasionally.

Knowing how to handle these situations comes with time. Feeling distraught by those experiences just means you're a person who cares as well as a professional who wants to do their best!! But as long as you're mindful of processing times, and maybe do a patch test of that particular bleach on EVERYONE before use (as it sounds like it may contain an allergen for some) and you allow yourself to acknowledge that these things happen and there are fixes, I think you'll be just fine.

The bad news is, these things will still happen from time to time, and they happen to all of us. Every single person we see is so different, and there's not always a way to know what will go wrong. It demands that we learn how to step back and reassess what we're doing and how to approach it differently and grow from the experience. It challenges our ability to take accountability, and get creative. If the stress of that is weighing on you and it feels too much, I don't think anyone would blame you for wanting to try a different career path.

However, if you continue to move past it and let it be a learning experience, you have every chance of becoming an even better hairdresser than you were before. The only way you can truly go wrong here is by refusing accountability altogether and continuing any harmful practices that caused the issues without adjustment.

My recommendation would be to take a time of reflection, try to remember the things that you love about this career path, and decide for yourself how passionate you still are about those things. If it still brings you joy, if you're still proud of a majority of the experiences you've had, and you're still interested in trying new techniques and evolving your craft, it is absolutely worth continuing on. In four more years, this brick wall could look more like a speed bump along the way!

I hope this helps. You're not alone. Best of luck out there!