Some hair weaving involve first relaxing the hair with chemicals that can cause severe burns if done incorrectly in order to ensure the weave and the natural hair blends properly. Some weaves are attached with adhesives that can also cause damage if used incorrectly. In both cases there is a potential for hair loss and disfigurement.

I think that's a good example of a field where lack of knowledge can be a very dangerous thing. I'd have thought like you until having seen first hand what some such hair products can do.

I'm sure there are unnecessary licensing. But I'm equally sure a lot of the licensing that seems pointless actually has reasonable justifications that are just not obvious if you don't know the field.