For me it was internal, stress and not eating right. The hair loss was pretty bad. It took a year for me to gain back the hair and I still feel like I'm not fully there yet. In the mean time when suffering from hair loss don't color, or use heat and other hair procedures i.e. relaxing, perming, thermal straightening or least drastically cut back. I take a multi for women, and trusty biotin (5000mcg) and recently reintroduced msm (2000mcg) back into my supplements. I'm gentle with my hair. Stick with sulfate free shampoos (except whenever I clarified), kept my naturally dry hair conditioned, trimmed, used coconut oil (which is one of the few oils that can penetrate and strengthen the hair shaft), tea rinses (strengthening).