There are many ways:
- Watch the water in the sink as you are rinsing, if it is cloudy the solution is still in the hair (when water is clear the solution is out).
- Feel the hair. If it is slippery the solution is still in the hair.
- Smell the hair. If there is still a perm or ammonia fragrance, continue rinsing with warm water. As a guide, rinse 5 minutes for chin length hair. For every additional inch of length, add another minute to rinsing.