No, he is actually right on the dust mite thing.
Our mattresses and our pillows are FULL (I mean millions and millions) of tiny mites that do indeed live off dead skin. Remember, even non-P people shed squillions of microscopic skin cells every day...these mites just live off them.
If you saw a magnified piccy of a pillow/matress/carpet you would be truly shocked...there is a whole eco-system going on!
Now, if you are the kinda person who is allergic to these mites, life is terrible for you. You will scratch and wheeze and have adverse effects. That is why you can buy special mattresses etc and buy special treatments for them. Some people's lives are miserable because of this.
But, IMO, the doc may well be barking up the wrong tree if he is putting intensely itchy P down to dustmites! P can itch like mad, particularly if you are flaring, using certain topicals or can't control your temperature in bed...
SJ