As long as you don't mess, used diapers aren't going to hurt you. Urine ("pee")is sterile- no bacteria, nothing funky will grow, you won't get "infected" with anything.
The worst thing that happens in the short term is ammonia. After a few days the natural decomposition of the urine produces some ammonia, which can be very irritating to your skin.
If you want to be in thick squishy diapers, but don't want to marinate yourself in old piss, then layering is your best bet.
CodyRush has a great system. Basically, use a single diaper for function, then put more on top for thickness.
Another approach is to puncture & layer your diapers. Poke/tear holes in a diaper so it leaks, then put another punctured diaper over it, maybe one more (or many more . . .). Finish with an xl-size premium diaper "topper". When you "change", you toss any layers that are funky or falling apart, add a fresh base-layer, then put the rest of the used diapers back on top. This way you get to enjoy the squish and funk of a well-used diaper, without being in direct contact with it.
P.S. @boobybird89: Some people do, some people don't. Some of us like to wear dresses, some like to mess, some only ever wear dry diapers and never use them . . . there's all sorts of people here.
