What’s the Mystery Behind the Urge to Scratch a Head Itch?

Solving the Missing Link in the Itch- Scratch Puzzle

Immune cells, such as mast cells and basophils—which are often known to cause itching and are associated with skin allergies—failed to do so after being exposed to bacteria. Neither did pro-inflammatory chemicals called interleukins or white blood cells, which are known to be triggered during allergic reactions in skin disorders including eczema and atopic dermatitis.

S. aureus which is stimulated by innocuous stimuli triggers a hyperactive response, a condition called alloknesis. Alloknesis is the itchy or pruriceptive sensation evoked by a stimulus that is normally non-pruriceptive. Alloknesis is common in patients with chronic skin conditions and also in anonymous conditions like itching from a wool sweater.

The stimulated S. aureus releases a bacterial enzyme called protease V8. This V8 protease enzyme works by activating a protein called PAR1, which is present on skin neurons that come from the spinal cord and send several signals from the skin to the brain, including touch, heat, pain, and itching (2^✔ ✔Trusted Source
Physiology and Pathophysiology of Itch

Go to source). This sets up a vicious cycle of itching, inflammation, and itching again.

The enzyme protease V8 was single-handedly responsible for initiating itch.

Beyond Itch-Scratch Cycle

The protein PAR1, which is triggered by S. aureus, is also connected to blood clotting.

Administering anti-coagulants stops the activation of the protein PART1 and subsequently curbs the crucial phase of the scratch-itch cycle. The therapy can reduce skin damage and alleviate discomfort.

These potential findings can retransform the design of oral medicines and topical creams to treat persistent itch associated with skin conditions linked to an imbalance in the skin microbiome, such as atopic dermatitis, prurigo nodularis, and psoriasis.

In conclusion, it is not necessary to have inflammation for the microbe to cause an itch, but the presence of microbes can ignite an itch and exacerbate inflammation on the skin.

References :

1. S. aureus drives itch and scratch-induced skin damage through a V8 protease-PAR1 axis – (https://www.cell.com/cell/fulltext/S0092-8674(23)01164-9)
2. Physiology and Pathophysiology of Itch – (https://journals.physiology.org/doi/full/10.1152/physrev.00017.2019)

Source: Medindia