The common skin bacterium Staphylococcus aureus can cause itch by acting directly on nerve cells.
The findings by scientists at Harvard Medical School (HMS) and based on research in mice and in human cells, help explain why common skin conditions like eczema and atopic dermatitis are often accompanied by persistent itch.
In such conditions, the equilibrium of microorganisms that keep skin healthy is often thrown off balance, allowing S. aureus to flourish, the researchers reported in peer-reviewed scientific journal Cell.
Up until now, the itch that occurs with eczema and atopic dermatitis was believed to arise from the accompanying inflammation of the skin.
But the new findings show that S. aureus single-handedly causes itch by instigating a molecular chain reaction that culminates in the urge to scratch.
“We’ve identified an entirely novel mechanism behind itch – the bacterium Staph aureus, which is found on almost every patient with the chronic condition atopic dermatitis,” said senior author Isaac Chiu, Associate Professor of Immunology in the Blavatnik Institute at HMS.
“We show that itch can be caused by the microbe itself.”
Experiments showed that S. aureus releases a chemical that activates a protein on the nerve fibres that transmit signals from the skin to the brain.
The team focused on ten enzymes known to be released by S. aureus upon skin contact.
The researchers eliminated nine suspects, showing that a bacterial enzyme called protease V8 was single-handedly responsible for initiating itch in mice.
Human skin samples from patients with atopic dermatitis also had more S. aureus and higher V8 levels than healthy skin samples.
The analyses showed that V8 triggers itch via the proteinase-activated receptor 1 (PAR1), which is found on skin neurons that originate in the spinal cord and carry various signals – touch, heat, pain and itch – from the skin to the brain.
Normally, PAR1 lies dormant, but upon contact with certain enzymes, including V8, it gets activated.
Treating animals with an FDA-approved anti-clotting medicine successfully blocked the activation of the protein to interrupt this key step in the itch-scratch cycle.
The treatment relieved symptoms and minimised skin damage.
The researchers said that their findings may inform the design of oral medicines and topical creams to treat persistent itch that occurs with various conditions linked to an imbalance in the skin microbiome, such as atopic dermatitis, prurigo nodularis and psoriasis.
The research opens up a new avenue for creating soothing skin care products, targeting S. aureus and its molecular chain reaction.
In the meantime, here are five cosmetic ingredients already on the market, claiming to help prevent that itchy feeling.
AntalGenics: Calmapsin & Capsisilence
Calmapsin claims to reduce sensitive skin signs and atopic tendency skin, while Capsisilence helps users achieve a healthy scalp. Calmapsin has a 360° effect over neurons and skin cells; it modulates the activity of sensory neurons reducing the itching sensation. In addition, it provides antioxidant activity protecting from oxidative stress, and improves skin barrier function. Capsisilence, meanwhile, calms itchy scalps by reducing the activity of the sensory neurons that are responsible for itchiness. It helps to diminish inflammation and scalp redness by acting on immune cells. Capsisilence also decreases dandruff reappearance by reducing desquamation.
BASF: Castaline
Active ingredient Castaline is 100% natural and organic, and derived from French chestnut leaves. It helps support the skin’s barrier function with visible and tangible effects. Atopic-prone skins are characterised by a cycle of immunological abnormalities that break down barrier functions, causing itchiness and redness, and which often lead to microbial dysbiosis due to a prevalence of S. aureus. In a double-blind, randomised in vivo study, 22 female and male adults with dry skin and a mild-to-moderate EASI (Eczema Area and Severity Index) score applied a base cream emulsion inspired by an established market reference product for very dry skin on one arm or hand, and the same emulsion containing 2% Castaline on the other arm or hand. After 56 days, the product containing 2% Castaline delivered a 27% decrease in transepidermal water loss (TEWL) compared with 18% when using the base cream alone. Additionally, the average EASI score decreased by 43% using Castaline. Also, since the French chestnut leaves are collected from young trees that do not bear fruit, the making of Castaline can be considered as using an agricultural by-product.
Jaka (Greaf): Calmnerv CR
Calmnerv CR targets the discomfort of sensitive skin and relieves symptoms including itching, stinging and burning. An extract of green fruits of Citrus reticulata (tangerine) from Quzhou, China, Calmnerv CR can effectively inhibit the activation of transient receptor potential vanilloid 1 (TRPV1) – the calcium-permeable ion channel known for its ability to be gated by a constituent of red chilli pepper – and consequently reduce extracellular calcium influx to relieve discomfort. Clinical studies show that 0.5% Calmnerv CR can quickly relieve the discomfort caused by 10% lactic acid and help to strengthen skin tolerance in seven days. It is recommended for use in sensitive skin products, or for use alongside ingredients which could bring irritation, such as phenoxyethanol, lactic acid or retinol.
Givaudan Active Beauty, Omegablue
Omegablue is created from upcycled wild bilberry seeds and used to revert skin dryness, irritation and desquamation caused by lipid barrier damage. The seeds contain 20% of linoleic acid (omega-6) and α-linolenic acid (omega-3) in an optimal ratio; these compounds are both known for their ability to improve hydration and skin barrier functionality. The efficacy of Omegablue has been shown in surfactant-induced depletion during clinical tests. After three days of damage, the treated area has completely restored the skin barrier function. Omegablue also performs well on skin with psoriasis, as it significantly decreases erythema severity, down to 27% and scales formation by 28% in four weeks. Even better results are shown on eczema challenged skin condition as erythema severity decreased by 37.5% and itch rating by 42.8%. Additionally, the PASI (Psoriasis Area Severity Score) and EASI are markedly ameliorated by 27% and 35%
Mibelle Biochemistry, SensAmone P5
SensAmone P5 is a biomimetic peptide that is based on a sea anemone protein which calms sensitive skin and reduces skin irritation. A unique protein in the venom of the leathery sea anemone acts as an inhibitor of the TRPV1 pain receptor, whose overactivity results in skin that can react strongly to harmless environmental stimuli with itching or even burning and redness. As the protein is unstable and too large to penetrate the skin, Mibelle Biochemistry developed a pentapeptide that contains the TRPV1 inhibitor sequence of the sea anemone protein. To ensure improved skin uptake, the peptide is incorporated into a soft sphere carrier system based on shea butter. An in vitro assay showed that SensAmone P5 reduced the activation of the TRPV1 pain receptor and inhibited it more effectively than the full-length sea anemone protein. In clinical studies, meanwhile, it reduced the electrical current perception threshold of the skin, which is an indicator for skin reactivity, and it decreased skin sensitivity by reducing the response to skin irritation.
Featured companies
- Companies:
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