I'll put a relaxer in my hair if I don't feel like waiting for hours in a hair salon to get my hair done. I did so a week or so ago.
I applied it and let it sit so that it could straighten. For those who don't know, after you put the relaxer in your hair, you're supposed to rinse it out, then wash your hair with neutralizing shampoo to stop the straightening action of the relaxer. If you do not use this shampoo, the relaxer can keep working and you will lose hair. Wanna know how I know this? When I was a little girl, my mom's hairdresser friend forgot to use the neutralizing shampoo (I believe that she was fresh out of beauty school), and I lost hair around the edges of my head. It grew back of course.
Imagine my surprise when I realized that I'd run out of neutralizing shampoo, and it was about time to rinse out the relaxer. If you let this stuff sit for too long, it will start to burn your scalp. It hadn't started burning yet, but I had to get some shampoo. And fast.
Luckily, there's a beauty supply store about 1 minute from my house. I walked in with my hair full of relaxer and shouted, "Neutralizing Shampoo?!". The owner looked at my head and grinned-he looked like he wanted to laugh his butt off-then went to the back of the store to get me a bottle. I went home and used it.
That'll teach me to make sure I have everything before I do it again.