My hands hurt a lot after they dry. Getting deep pressure on my hands helps. I've learned methods of self massaging my hands to help me through after a shower. It's worse if I use soap, not quiet as bad if I use a body wash than if I use a true soap.
Getting me to actually wash my hands... yeah, that's not a thing that happens. It's not worth it. I've not had issue with my health, and I instead am not spending all my time only focusing on trying not to
chew my hands off. I still need to do that a bunch, but I'm able to do other things. If I were to wash my hands every time I'm "supposed to", then I'd not be given that option.
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For suggestions:
-Look into alternate ways to apply deep pressure. If he's sitting on his hands, it definitely seems likely to me that he wants deep pressure on his hands. I'm looking into getting myself arthritis gloves to see if they help, but haven't done that yet. I do exercises that work my hands, like with theraputty, and that helps. I squeeze my hands tight, and massage them with each other.
-How dry is the air in your area? I find my skin is most painful when the air is drier.
-Wilbarger brushing protocol. (But finding coping skills is necessary even with this)
-Do use a better soap; even if its not everything, getting as many little bits easier helps. Even if he only washes his hands a little, making those few times as easy as possible is important
-check water pressure (in terms of asking him); is it easier to use it when its harder pressure or softer pressure? I've seen both.
Hearing sensitivity:
-Get him some earplugs, let him use them for part of the day. (But not all of the day, if its too long your brain can adapt and make it so it expects you to always wear them, so not more than half of the day); the musicians ear plugs are ones I've generally heard recommended for if he's to wear them at school because they distort sound least. I have a pair of them and find them less itchy than foam ear plugs.
-I really liked doing the therapeutic listening program; it helped me with so many things; unfortunately its frequently one of the most expensive programs so you need to take that into account.
To help you understand what your son might be dealing with, here is me describing what a shower is like for me, and why I avoid showers. After a shower, for at least 24 hours, my hands are in pain, like my skin doesn't belong on my body, but that's after a shower itself which is already an extremely overloading experience.
http://turtleisaverb.blogspot.com/2014/02/a-shower.html
Hope that's a little helpful. If you have other questions, I'll try to answer them.