The Croton or Codaieum is in the Euphorbiacae family and as such these plants are commonly found to have a free flowing juice or sap with toxic or irritating compounds. Anyone working with Pencil Cactus, Poinsettia or Crotons knows that the sap or juice will stain clothes badly and cannot be removed. Extensive work with these plants requires old clothing, and possibly hand/arm protection.
At first when finished working with Crotons with bare hands, there's not likely to be any sign of allergy/sensitivity. This shows up a bit later if/when you haven't washed your hands, and after having scratched a neck itch or rubbed an eye, itchy hives present themselves on that skin. If so then going forward you'll either have to remember to immediately wash your hands with soap and water before touching bare skin (alcohol-based hand sanitizer is not effective) or perhaps it's easier just to start out using garden or disposable gloves when working with these plants.
The chemical compound found in the Croton sap and associated with contact dermatitis is:
This compound is part of the plant’s natural defense system and if ingested in small doses will cause pain and discomfort. If the skin is repeatedly exposed to this sap, a rash can easily develop (just like Ficus sap). Surprisingly one of us is sensitive, the other not at all. If you are sensitive, we recommend long sleeves, gloves, frequent washing with soap and avoidance as the first line of defense. If a rash develops, we have found 2.5% hydrocortisone cream beneficial and as a last result, a physician directed treatment of oral cortisone steroids. It’s a nasty rash on the arms and neck that we have learned about the hard way.