01What is genuinely established
Human skin is not sterile and is not meant to be. It carries a resident community of bacteria, fungi, viruses and mites, distributed differently across oily, moist and dry sites. The composition varies between individuals and shifts with age, environment, occupation and washing habits. Sequencing technology over the past two decades has characterised this in considerable detail, and none of it is in dispute.
What is also reasonably established is that the skin surface environment, particularly its mildly acidic pH and its lipid content, both supports that community and depends on it. Interventions that raise surface pH or strip lipids change the environment, and repeated disruption is associated with impaired barrier function.
02Where the marketing takes a leap
From that foundation, the category makes a jump that the evidence does not yet support: that a specific cosmetic product can restore, balance or optimise the microbiome, and that doing so produces a benefit a user would notice.
Three problems sit in the way. The first is that there is no agreed definition of a healthy skin microbiome against which to measure restoration. The second is that measuring a compositional shift is not the same as demonstrating a clinical or cosmetic benefit. The third is that microbiome friendly is not a defined term with a test behind it, which means two products carrying it may have done entirely different things to earn it, or nothing at all.
03The part you can actually act on
Strip away the product claims and a practical instruction survives, which is roughly: stop attacking your skin. Wash with something mild, at a pH close to skin, once or twice a day rather than five times. Do not use antibacterial products on the face without a reason. Do not scrub. Do not use alcohol heavy products on abraded skin.
That advice is compatible with the microbiome literature, with basic barrier science and with NHS guidance on acne, and none of it requires buying anything with the word microbiome on it. This is the recurring pattern in the category: the actionable finding is free, and the products are sold on top of it.
04The squeaky clean feeling, decoded
The tight, squeaky sensation after washing is produced by lipid removal and a raised surface pH. It is a sensation of damage, not of cleanliness, and the association between the two is a learned marketing artefact rather than a physiological fact.
Men are particularly exposed to this because the male grooming category has historically sold intensity: deep cleansing, purifying, oil control, charcoal, menthol. Those cues sell well and describe products that are often too aggressive for daily facial use. The cleanser argument in full is in what a face wash is made of.
05Acne, and the bacteria that is not the enemy
Acne involves Cutibacterium acnes, an organism present on essentially everyone's skin. It is not an infection in the ordinary sense, and eliminating the organism is neither achievable nor the goal of treatment. The condition involves follicular blockage, sebum, inflammation and the microbial component together.
This is why the intuitive response, which is to wash more and use antibacterial products, tends to make acne worse rather than better, and why NICE guidance and NHS advice both emphasise appropriate topical treatment over aggressive cleansing. Persistent acne is a condition with effective treatments available through a GP, and treating it with cosmetics indefinitely is a poor use of time.
06The fungal side, which men encounter more
Malassezia yeasts are normal residents of skin and are implicated in seborrhoeic dermatitis, which produces the flaking and redness common on the scalp, in the eyebrows, beside the nose and under beards. It is more frequently symptomatic in men.
Here the microbial community is genuinely central to a common complaint, and the interventions with evidence behind them are antifungal, not microbiome balancing. This is a useful illustration of the difference between the science being relevant and the marketing being supported. The scalp version is covered in the shampoo question.
07Antibacterial products, and where they belong
Antibacterial washes and hand sanitisers have clear uses in specific circumstances. Daily facial washing is not one of them. Routine use of antimicrobial products on healthy skin has no demonstrated cosmetic benefit and carries the general concern about antimicrobial resistance that public health bodies apply across the board.
The pandemic normalised frequent sanitiser use and produced a visible wave of irritant hand dermatitis, which is a useful reminder that the barrier responds to repeated disruption regardless of how good the reason is. On hands, an emollient after washing solves most of it.
08Should you buy microbiome products
If a product with a microbiome claim is a well formulated mild cleanser or a decent moisturiser at a price you are happy with, buying it costs nothing but the premium. If it is priced substantially above equivalent products on the strength of the claim, you are paying for a hypothesis.
The specific claims worth treating with most suspicion are live cultures in a preserved product, which is a formulation contradiction, and any suggestion that a cosmetic will treat a condition. The latter crosses from cosmetic into medicinal claim territory, which is regulated in the UK, and is covered in phrases with no fixed meaning.
09An area to watch rather than to buy into
Skin microbiome research is one of the more genuinely interesting areas in dermatological science, and it is plausible that useful interventions will come out of it. The current position is that the science supports a set of behaviours, most of which are free, and does not yet support the product claims built on top of it.
We will revise this position when the evidence moves. That is what our assessment criteria commit us to, and it applies to ingredients we currently rate well as much as to those we do not.