Brushing does not aggravate hair loss; it is best to brush hair starting with the ends, and you should use a detangling product on long hair.
If you're experiencing hair loss, your hair will fall out more easily during brushing, which is normal. Brushing eliminates dead hair.
Excessive brushing can be harmful since it can damage the scales of the hair cuticle (the hair surface) or put repeated pressure on the roots.
For long hair, it's best to use detangling conditioners and to begin brushing at the distal ends while holding the base of the hair to avoid pulling on the roots.