What is this rash?

[MrsBungle]

My 4 year old ds has woken up with a rough to touch pin prick rash this morning on both arms, feet, knees and legs.

It is not on his face, chest, back or stomach.

Some of it is red (he says he's not been scratching and it's not itchy) and some not.

He is very well in himself. Any ideas?

Thanks for any help.

My DS gets a very similar rash, on his elbows, knees and inside his thigh. He has sensitive skin, and it's a form of eczema. It usually flares up if he is hot, if I have changed the soap, fabric softener, if he has new sheets or new trousers, generally a skin irritant. E45 seems to help, with him it never really lasts long, and I have an increasingly long list of things that set him of to avoid.

Thank you sugar plum, that's really helpful.