Norma is right, with the correct formulation and the right dough management procedure there shouldn't be any need for a dough relaxer, but for those times when we just can't make our pizzas without them we have a number of them to select from.
Garlic and onion (powder or flakes) is a pretty decent dough relaxer especially well suited for those times when the dough just needs a little encouragement to open into a pizza skin.
For those time when more encouragement is needed, especially when we're making no-time or short time doughs something with a little more "oomph" is needed, this is where we get into L-cysteine (commercially available as PZ-44) or glutathione (dead yeast). You have to be careful with these last two since they can/will liquefy a dough if used at excessive levels. In the pure form this translated to about 90-parts per million based on the flour weight, but thankfully, there products are commercially blended to make scaling much easier so we're looking at 1 or 2% of the flour weight when used in a commercial ingredient blend. When used within the recommended use levels, you will never know it is there in the finished crust, but if used at excessively high levels, assuming you can handle the dough, which is now very soft and sticky, the finished crust can impart a slight stinging or tingling sensation to the lips as the crust is eaten. This closely mimics the effect of thirst on the lips (yes, you will be licking your lips), but that's about the extent of it. If you are holding the dough over in the fridge for several days, you might end up with an overly soft, unmanageable dough that has been so weakened by the reducing agent that the finished crust takes on a flat, poker chip appearance with a knife edge. Plus, if the dough cannot support the weight of the toppings, it will collapse in the center section resulting in a beautiful gum line. How do there things work? The work by breaking the protein molecules at their bonding points (sorta like taking a bicycle chain apart by removing the master link(s). This can be reversed to a great degree by using an oxidizing agent such as ascorbic acid, or potassium bromate, just to name a couple. Enzymes (protease enzymes) can also be used to achieve the same end result but unlike L-cysteine and glutathione (both are amino acids/protein building blocks) the enzymes hydrolyze the proteins so they are no longer proteins, hence the dough softening resulting when protease enzymes are used cannot be reversed, plus, the enzymes have a nasty habit of continually working to hydrolyze the proteins, so they just don't stop working in most cases. This can make long term management of the dough in the cooler much more tricky, and management of scrap dough is all but impossible. Excessive use levels will easily turn a dough into a bucket of slime way before you Will ever have enough to impact the finished flavor of the crust. Think of it like this, when we imbibe in a little relaxer it can be good for us, but too much can result in unwanted problems, the same can be said for relaxers and dough.
Have a great day, and use those relaxers in moderation.
Tom Lehmann/The Dough Doctor