Canker sore: A canker sore, also known as an aphthous ulcer, is a single pale or yellow ulcer with a red outer ring or a cluster of such ulcers in the mouth, usually on the cheeks, tongue, or inside the lip.
The Board will allow a maximum temperature of 120 degrees Fahrenheit. Hand sinks in commercial kitchens are only used by employees. These employees are typically washing and rinsing pots and pans in pot sinks which could have 140 degree water. Those pot sinks, in some kitchens are located right next to the hand sinks.
Read http://barfblog.com/2014/03/no-is-hot-water-more-effective-for-washing-hands/ for an answer. Other research articles I have read have indicated that cold water closes the pores and hot water runs the risk of scalding. 35 to 40 C seems to be a good temperature.