The most common and effective exfoliators are derived from alpha-hydroxy acids (AHAs). However, they can irritate sensitive skins and with frequent usage, the effectiveness levels off; the skin has the ability to adapt to treatments with "accommodation response".
In 1995, fruit enzymes began to be used as a gentler alternative to AHAs. Papaya and pineapple are the most effective and common in cosmetic use, with an almost neutral pH of 6.5. AHAs and enzymes perform different functions to achieve exfoliation; that is, to remove dead cells on the skin’s outer layer. AHAs loosen and lift the top layer of dead cells, primarily composed of keratin (a protein), while proteolyitc enzymes dissolve it. Enzymes, unlike AHAs, don't encourage new cell growth.
It is difficult for cosmetics companies to formulate with enzymes since they are highly sensitive to solvents and tend to break down, losing their effectiveness very quickly. However, when stabilized, enzymes can serve a catalytic function and help improve the activity of other ingredients in a formulation.
The big commercial cosmetics companies such as Chanel and La Prairie are developing products that combine AHAs and enzymes. Meanwhile, over at Estee Lauder, research is being done to find molecules that will work with enzymes to make them behave more like AHAs.
I use Tracie Martyn's Enzyme Exfoliant. I like it, but I don't love it (as Susan Sarandon purports to). so far, though, I haven't found anything better.
A patent has been filed for a toilet paper containing pineapple enzymes to aid sewage purification.
Bromelain is the name for the enzyme found in pineapples, It is used as a dietary supplement to aid digestion. It may also boost the immune system.
Taking a whole bottle of bromelain supplements before you go to bed will not make you wake up looking as if you've had a facelift. Nevertheless, there is at least one person who keeps trying and posting his lack of success on an online message board.