I probably wont use AHA and/or retinol. That may make the situation worst.
Has he been seen by a derm? depending on how bad it is it can range from requiring steroid creams to highly emollient creams. Depending on types or triggers
For something over the counter: I would opt for gentle products like baby washes, emollient creams. etc
Avene Xera Calm Balm or cream is great.
Ingredients like colloidal oats, ceramides are great too,
AHA/Retinol will irritated the already irritated, inflammed or crusty skin