Cultivating a Healthy Skin Microbiome

A company is marketing a probiotic spray designed to help cultivate a healthy skin microbiome.  The spray contains Ammonium Oxidizing Bacteria (AOB; specifically the genus Nitrosomonas) that derive their energy solely from consuming the ammonia and urea found in sweat.  Supposedly, if you have enough AOB, you don't smell bad because they consume all your sweat, releasing beneficial nitric oxide gas!



I wanted to learn more about the skin microbiome, and found this comprehensive article with diagrams to show skin follicles, etc the complex topography and ecology of the skin environment.

These new data are based on DNA assays, and with improvements to these techniques, viruses, mites, and fungi are also being inventoried. This is certainly an improvement from the old days when only culturable bacteria were studied.  Here is a classic paper about the microbial correlates of dandruff.  Apparently there is no cause of dandruff, but simply a feedback between bacteria and fungi and the scalp. A fungus called Malassezia spp can release compounds that stimulate epidermis to proliferate.    Fungicides cure dandruff by killing the Malassezia spp, but many people harbor Malassezia spp without dandruff.   Perhaps an "ecological" cure could involve cultivating probiotic bacteria?

The same article also has the classic diagram showing different microbial communities on different body parts, based on their temperature, moisture and oilyness (sebum versus apocrine ).

Interestingly, soap and shampoo may be destabalizing our skin microbiome, in the same way that antibiotics can impact the gut microbiome.  For example, many ingredients in personal care products have been found in laboratory tests to inhibit "good-guy" AOBs, including sodium lauryl sulfate (SLS is one of the harshest detergents), sodium coco-sulfate, and even castile-type soaps. (Source)

To maximize ammonia utilization, AOBsproduce unique enzymes on elaborately folded cell membranes. These membranes are intricately folded so that they can increase the surface area for ammonia-oxidation. This means that they are able to boost both their ammonia-oxidizing capacity and their energy output.  However, this elaborate membrane architecture also renders AOBs particularly sensitive to membrane-disrupting chemicals, such as anionic surfactants found in modern soaps and detergents.

Detergents replaced simple soap in our hygiene routine soon after WWII and form a major part of most bath products. Anionic detergents such as lauryl sulphates, sarcosines and sulfosuccinates can be harsh to the skin and especially the microbiome.

When reading the ingredients list on your cleaning products, you can identify anionic surfactants as those that have the following in their names:

Sodium
Ammonium
Magnesium
Sulfate
Sulfonate
Gluconate

(For example, sodium laurel sarcosinate, magnesium laurel sulfate, and sodium gluconate.)

Nonionic surfactants are gentler to the skin microbiome, although not entirely harmless. (Source) They include:

Ethoxylates
Alkoxylates
Cocamide

All of my soaps and shampoos contain these ingredients, except for Black African soap "made from shea butter and palm kernel oil mixed with ashes".  The detergent in this soap is laurel glucoside, (AKA dodecyl glucoside) a non-ionic surfactant molecule.  Because it is non-ionic, it is a milder detergent, often used in cosmetics, shampoos, etc. Glycosides are produced from lauryl alcohol and glucose.

It may be possible to specially order detergents from companies like this one.