Kitchen Hint: keeping cleaning sponges fresh with real soap

Kirk's Castile bar soap

Kirk’s Castile bar soap

By Catherine Haug, Sept 30, 2015 (Photo, right, from Amazon (4))

Do you use sponges in your kitchen and bathroom for cleanup jobs? Synthetic sponges tend to get rather smelly after only a few uses, even if you rinse them well. That smell comes form bacteria living in the sponge. A NSF International survey of sponges in U.S. homes found 77 percent of the sponges and dish cloths contained coliform bacteria, 86 percent had yeast and mold, and 18 percent had Staph bacteria. These are what produces the smell.

Another NSF International study in Michigan found that kitchen and bathroom sponges are the ‘germiest’ places in the home. Next in line in the study: toothbrush holders, pet bowls, kitchen sinks -especially the drains, and the coffee reservoir where you pour the water to be heated (5). What’s the best cleaner to rid these places of bad germs?

This hint is from Cat; read on for more.

Cat’s Kitchen Hint

I’ve tried boiling sponges with baking soda, which removes the smell for a day or so, but they quickly become smelly again.

My suggestion is to keep a bar of handmade soap or Kirk’s Castile soap in a soap dish near your kitchen or bathroom sink. After each use, rub both sides of the sponge on the bar; rub the soap in with your fingers and rinse well, then squeeze to dry as much as possible. This freshens the sponge without much time or effort expended. It also works well with sponges that have a scrubbing surface on one side.

This type of soap is also excellent for cleaning cutting boards, knives and other equipment used when cutting up fresh meat and chicken which may harbor bad bacteria. Then spray with diluted vinegar, which helps to remove the soap and also has anti-bacterial ability.

For cleaning sinks and sink drains, rub your damp sponge with a bar of soap; work the soap into bubbles by rubbing the sponge with your fingers. Then use that soapy sponge on your sink and its drain, and also the drain basket. Let the area rest for a couple minutes, then follow with a spray of diluted vinegar.

How does this work?

Real soap (handmade, Dr. Bronner’s or Kirk’s Castile) is a natural antimicrobial substance that attacks bad bugs while leaving the good ones alone. It’s the bad bugs that create the smell, and the soap keeps those critters in check.

I do not recommend using dishwashing soap/detergent, commercial liquid hand-soaps and most commercial bar soaps for this purpose. These do not contain real soap but rather detergents and surfactants that do not have antimicrobial ability.

Some of those products have synthetic anti-microbial substances added (e.g., Triclosan, triclocarban, and chloroxylenol and tetrasodium EDTA (3)), but these substances, such as triclosan, are in large part responsible for antibiotic-resistant bacterial diseases that are becoming rampant.

You might also be tempted to use hand-sanitizers to rid  your sponge (or your hands) of bacteria. These products are primarily comprised of alcohols such as rubbing alcohol which are readily absorbed through the skin into the blood stream where they can cause problems. Plus they kill not only the bad bacteria but also the good bugs that help keep bad bugs away.

Concerning triclosan, the FDA is currently giving it a closer scrutiny. Also, a recent study (1) comparing antibacterial ‘soap’ with plain hand soap used with room-temperature water and with warm water, found:

Results: There was no significant difference  in bactericidal activity between plain soap and antibacterial soap at either test temperature. However, antibacterial soap showed significantly greater bactericidal effects after 9 hours. These results suggest that although triclosan-containing soap does have antibacterial activity, the effects are not apparent during the short time required for hand washing.

Conclusions: Antibacterial soap containing triclosan (0.3%) was no more effective than plain soap at reducing bacterial contamination when used under ‘real-life’ conditions. The present study provides practical information that may prove useful for both industry and governments.

Furthermore, these synthetic antibacterial ingredients may be harmful for human health. Triclosan has been implicated in problems related to disrupted hormone functions in study animals, which hints that the same issues may happen to humans. Additionally, triclosan is known to cause problems in humans, such as

  • estrogenic activity that stimulates growth and development of cancer cells in cases of human breast cancer;
  • impairment of muscle function in both humans and animals;
  • linked to an increase in allergies among children;
  • help staph bacteria colonize in the human nose.

Popular cleaning method that doesn’t work (per USDA studies quoted in a Nutrition Action article (5)): Soaking in 10% bleach or lemon juice (however, a stronger bleach mix – 3/4 cup in a gallon on water – is very effective, but is more bleach than  what most people are willing to do.

Popular cleaning methods for sponges that do work (per USDA studies):

  • Microwave at full power for one minute was the most effective way of killing the bacteria in the sponges. However, don’t microwave a sponge that contains metal for scrubbing. Also you need to microwave the sponge after each use
  • Running through a dishwasher; it’s the boiling, steamy environment that cleans the sponge, but it needs to be done after each use of the sponge. For me, it’s just easier to use the soap each time.

NOTE: the USDA did not test using real soap as in this kitchen hint, but if they had, I’m confident – as a chemist – it would have produced good results, because the microbes they found in dirty sponges (coliform and staph bacteria, yeast and mold). There’s a very good reason why handmade soaps have been used for millennia – because they not only clean surface dirt but also microscopic bacteria that live inside the sponge’s many chambers.

See also:

Cat’s  related articles on The EssentiaList:


  1. Bactericidal effects of triclosan in soap both in vitro and in vivo, by SA Kim,; J Antimicrob Chemother. 2015 Sep 15. pii: dkv275.(
  2. Mercola, Antibacterial soap is all washed
  3. Wikipedia:
  4. Amazon:
  5. Nutrition Action:  and


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