Yes. Developer can damage hair. If you pick a developer that is too strong for the hair texture of your client, it has the possibility of lifting the cuticle so much that it can't be smoothed back down.

What happens if you just put developer in your hair?

Applying 20 volume developer to your hair causes the cuticle cells to swell and lift up. ... Without bleach, 20 volume developer alone can lighten your hair by about one level. So if you're currently a level 5 light brown, using 20 volume developer alone can lighten it to a level 6 dark blonde.

Is 30 Developer bad for your hair?

Should I Use 30 or 40 Volume Bleach? If your desired hair color is not more than two to three shades lighter than your natural color, you should use a 30 volume developer. The strongest developer, 40 volume developer, can dramatically alter your hair's color and cause permanent damage if used incorrectly.