I don't know how it works...but it works! I have spent hundreds on all the other products...Bissell, Hoover, Dyson, Rug Doctpr. Zeb & others in an attempt to remove spot stains accompanied by urine odor. One particular area in our home I must have used my carpet extractor machine (a very nice one) at least 15 times on the spots. But no matter what I used, with or without my machine, the spots kept coming back and the odor was horrible. When I saw this product and read its reviews, I admit it, I was skeptical and thought to myself, "Yeah right, this will be another waste of money." Well I am here to tell you...this stuff really works on both fresh accidents and long time stubborn stains and odors. And it could not be easier to use! It is more expensive than most products that make the claims that this one does. But, I swear, this one actually works if you use it exactly as instructed. Those stubborn stains and odors I had dealt with for months and months are gone now finally. It took two applications of this product, which didn't surprise me. But I can now say that the recurring stains and that awful urine odor are finally 100% gone! It completely dissolved the stains AND odors. It has been weeks since I used this product and even with my nose down on the carpet, there is not a trace of odor or stain left. Try it. It will be the last product you will ever have to buy and it is well worth the money...every penny!