Hi. I'm online and happy to answer your question today.
The most common cause this time of year is eczema. You could try some 1% hydrocortazone cream 2x/day to the affected area. If this doesn't help then I'd take him in to see his pediatrician.
Does this make sense to you?
And, now, the obligatory word from our sponsors: :o)
I hope that this information was helpful for you. Please, allow me get credit for my time and effort in assisting you and press the ACCEPT button for this assist. I will be glad to answer additional questions until you are satisfied. Thank you very much. Positive Feedback and/or Bonus is welcomed and appreciated.