Herbal extracts help restore the skin microbiome balance

The skin is a complex system, with about a million bacteria living on each square centimeter. In a healthy state, this microbiome helps maintain the skin’s protective barrier and regulates immune responses. When the balance is disrupted (known as dysbiosis), pathogenic or opportunistic species, such as Staphylococcus aureus, which causes skin and soft tissue infections, or Cutibacterium acnes, associated with acne, may become more prevalent.

Today, broad-spectrum antibiotics, retinoids, and other antimicrobial agents are often used to combat such microorganisms. However, this approach has significant drawbacks. These medications can not only eliminate harmful bacteria but also beneficial ones, potentially leading to antibiotic resistance. In some regions, nearly 46% of staph infections on the skin are caused by methicillin-resistant Staphylococcus aureus (MRSA). As a result, dermatologists are increasingly seeking alternatives, focusing on strategies that aim to restore the natural balance of the microbiome rather than eliminate it.

In a new study, the team studied the potential of eight plant extracts as prebiotics for the skin, i.e. substances that can selectively stimulate the growth of beneficial bacteria and suppress pathogenic ones. The list included extracts of onions, garlic, flaxseed, guduchi, mango ginger, as well as cabbage, ashwagandha, amla and terminalia.

Experiments were carried out in vitro on bacterial cultures. Scientists evaluated how the extracts affect the growth of three key strains: the useful S. epidermidis and pathogenic S. aureus and C. acnes. To do this, the growth kinetics of bacteria were monitored over a period of 48 hours, changes in cell membranes were analyzed using high-resolution scanning electron microscopy, and the profile of metabolites was studied. The antioxidant activity of the extracts and their safety for human skin cells were also evaluated.

The study revealed that a number of extracts had a dual effect, as they simultaneously inhibited the growth of pathogens and moderately supported the growth of beneficial microflora:

• flax and garlic extracts completely stopped the growth of S. aureus after 6 hours of incubation. These extracts caused the bacteria to contract and lyse, while other extracts caused swelling, wall ruptures, and membrane perforation;
• mango ginger extract at a concentration of 0.625 mg/ml reduced the number of viable C. acnes cells by 99.9% in 15 minutes;
• onion and guduchi extracts promoted the growth of S. epidermidis. The most effective was onion – it increased the population by 4% in 24 hours at the same concentration of 0.625 mg/ml;
• extracts of leaves and stems of guduchi gave an increase of about 1-2%;
• in cultures of S. epidermidis stimulated by onion, the level of butyric and succinic acids – short-chain fatty acids (SCFA) that are known to inhibit the growth of S. aureus and pathogenic variants of C. acnes increased;
• at a tenfold lower concentration, extracts of onion and guduchi stems did not show cytotoxicity for human keratinocytes in the experimental conditions.

The data obtained are still only in vitro results, but they help to form a number of important conclusions. It is possible to consider the use of an ecological approach based on the natural competition of microorganisms. Plant prebiotics can become a component of products that do not destroy the microbiome, but help it to recover.