Overview
Hexavalent chromium is the Cr(VI) oxidation state of chromium, and it is carcinogenic when inhaled. Ordinary trivalent chromium, Cr(III), is much less harmful, so the restriction targets the hexavalent form specifically.
Where it's restricted
RoHS caps hexavalent chromium at 0.1 percent by weight per homogeneous material. It is also restricted in vehicles under ELV.
Several chromium(VI) compounds, including chromium trioxide and dichromates, sit on the REACH Authorisation list, which means their use needs specific authorisation. See the REACH annexes reference for how authorisation works.
Typical uses
Cr(VI) has been used for corrosion-resistant coatings and passivation layers, and in surface treatment of metals. Trivalent alternatives have replaced it in many of these processes.
Only the hexavalent form is restricted. A chromium plating or coating can be compliant if it uses Cr(III) chemistry rather than Cr(VI).
Note: this is general educational information and not legal advice. Check the official source before relying on it.