Are there any common ingredients in soap, lotions/creams, shampoo and toothpaste that can cause an allergic reaction?

I have been reacting to common grooming products for a while, now, mostly with itching and hives. At first I thought it was just my sensitive skin, so I switched to a less complicated moisturizer from the health food store by my house.
Then I realized that I was reacting to soap and shampoo, so I switched to an uncomplicated “natural” soap bar and sulfate free shampoo and conditioner. That seemed to help.
Now something is wrong with my mouth. I did switch to Sensodyne toothpaste two days ago (from Colgate Total). I had dental work done a few times over the last month, and my teeth and jaw have been very tender, I thought a toothpaste for sensitivity would help. Unfortunately, I seem to have reacted negatively to the toothpaste, my mouth is raw and swollen, like I would expect from an allergy.

Is there a common ingredient that I should know about? When I try to do a search, it just gives me a lot of sites about how toothpaste is destroying my health and how commercial soap is toxic and evil. That’s fine, and all, but not really what I’m looking for, heh.
Thanks.