I heard vinegar neutralizes the pH of urine. It that right? No. A lot of parents know vinegar helps when they wash diapers, but why? I asked my in-house scientist about the effect of vinegar as it relates to washing diapers. He writes:

Urine can fall in the pH range of 4.5 - 8, but is usually closer to 7 (which is neutral). The pH of urine only departs significantly from neutral when the body is having to process a lot of sugary food (goes acidic), or if a bladder or kidney infection is present (goes alkaline). If the alkaline condition were present then the vinegar would neutralize the urine, but this would be an unusual circumstance.

Ammonia is not present in urine (unless you have certain kinds of infections), but urea is present. However, once urine has left the body, bacteria in the air start to convert the urea component (which is acidic) to ammonia, which is very alkaline. So, unless you dump wet diapers immediately from baby into the washer, when you wash diapers you are really removing ammonia that has formed since the baby wet the diaper. The effect of ammonia formation is very apparent when you take off baby's nighttime diaper. Especially if the baby has wet early in the night, by the morning plenty of ammonia has formed. I recall many eye-stinging diaper changes in the morning.

As far as vinegar is concerned, it would work to neutralize any ammonia that has formed. This would be helpful because it appears that most detergents (not soaps) are formulated to work best at pH values close to neutral. A lot of ammonia could raise the pH and reduce the effectiveness of the detergent. Vinegar's main role in cleaning appears to be lowering the pH, so that if you were using soap (as opposed to detergent) any alkaline soap residues could more easily dissolve in the wash. The same effect dissolves mineral residue if you have hard water.

Conclusion: Since detergents work better close to neutral, the sooner diapers are washed after they are removed, the better your detergent will clean. Vinegar is good when the soiled item is alkaline - quite likely if the wet diapers have been sitting around and the urea has begun to convert to ammonia.

by Marc Pehkonen
copyright © 2005 Marc Pehkonen. Used by permission.