My 7yr old son has had diarriea for over 10 days now. his bottom is now red. he will still eat and drink and is still normal no other symptoms.

Long time: 10 days - it might be time to bring him to his doctor to see if there is a treatable cause of his diarrhea. Some viral causes can last that long- however, you seem concerned- and his red but may be related to a change in the colon from the diarrhea. Your doctor might also be able to give advice on how to deal with that.

Diarrhea for ten : Days is too long without intervention. Red bottom is going to get worst due to the acidic environment from diarrhea itself ! You can apply an antacid suspension on the affected areas to make it more soothing . Make sure it is not just irritated . The skin may be infected with bacteria or yeast. Get it checked out and start treatment early before it is too late.

Diarrhea : Prolonged diarrhea in a child should be evaluated and the child's hydration status should be checked by a physician