We think my DS2 is Lactose Intolerant, we never picked it up when he was little as they were FF Lactose Free formula but since switching to cows milk he started to have vile acrid BM's (up to 5 a day) which would literally burn his bum - not nappy rash but scalding from the acid. We also noticed that when he would do a BM he would pass alot of undigested food as well - like it was going straight through him. We switched him across to Lactose Free Cows Milk and Lactose free yogurt about 3 weeks ago and after a couple of days he started to doing formed BM's and only 1 maybe 2 a day and has only had 1 instance of burning poo (which was probably from him being on antibiotics recently which would have upset his gut) so we are just going to continue along the Lactose Free path with him for the time being