Teasing or backcombing is most definitely harmful to hair. When a an undamaged) hair fibre is viewed under the high magnification of certain microscopes, you can see that the cuticle cells all point downwards.
These cells are like hair’s armor, protecting its core. Teasing or backcombing goes against the direction of the cuticle cells, so the action can create damaged hair or completely strip cuticle cells from the hair fibre . Rather than creating lift and volume through this damaging practice, hairstyling products can be a much less damaging alternative to backcombing.