Dear Andrew,
The "sumac family" you mentioned is indeed the one the
Mango is in, although it's more properly known as the Cashew
family (Anacardiaceae). The bark, leaves and peel of the mango
contain a white, sticky sap that can cause an itchy rash. Also,
the small, reddish-white flowers exude a volatile substance that is
irritating to the respiratory tract. People who are known to have bad
allergic reactions should stay away from it.

Best Regards,
James