Hair products can be full of chemicals unnecessary for doing the job.
Any common hair care brands, including some of those used in salons, use harsh ingredients that strip your hair when shampooing, which makes the hair shaft vulnerable to damage, then coat it when conditioning which gives a false impression of healthy hair.
Nasty chemicals like Sodium Lauryl and Laureth Sulphate (SLS and SLES), Cocoamidopropyl Betaine (CAPB), parabens, silicones and toxic petrochemicals are used. ?Some of these, like SLS, SLES and CAPB are actually plant-based, which means they're even used by some 'green' brands. But SLS & SLES can be nasty on your skin.
They are known skin irritants (in fact SLS is held up as the industry benchmark for skin irritancy). What's worse is that they also break down your skin's protective barrier so let other chemicals get in and do more damage. CAP B is another nasty skin irritant that was actually voted Allergen of the Year in 2004 by the American Contact Dermatitis Society.
Showering is a time when your skin and scalp is most susceptible to chemical exposure, given the heat from warm water opens your pores up more. When washing your hair, the lather from your shampoo is not only being massaged into your scalp, it's also on your hands, face and entire body.