Skin Barrier & Itch-Scratch Cycle Simulator

Skin & Environment

Filaggrin function 40%

Ambient humidity 30%

Treatment

Emollient (barrier repair) 0%

Topical corticosteroid 0%

Live Readouts

Status: —

TEWL

0.0 g/m²/h

Barrier integrity

Inflammation

Itch level

How it works

The stratum corneum is a "brick and mortar" wall: corneocyte "bricks" held together by lamellar lipid "mortar", assembled from filaggrin breakdown products. When filaggrin is deficient (as in atopic dermatitis, often from FLG loss-of-function mutations) the wall becomes leaky, so water escapes and irritants/allergens penetrate more easily.

Barrier integrity B = clamp(0.3 + 0.007·Filaggrin + 0.005·Emollient − ScratchDamage, 0.05, 1)

Transepidermal water loss (Fick's-law form):
TEWL = 4 + 60·(1 − B)·(100 − Humidity)/100     [g/m²/h]

Inflammation I = clamp((1 − B)·100 − 0.6·Corticosteroid, 0, 100)
Itch  = clamp(1.5·(TEWL − 6) + 0.4·I, 0, 100)

The itch-scratch cycle is a positive-feedback loop: high TEWL and inflammation raise itch, scratching mechanically breaks the barrier further (ScratchDamage jumps up), which raises TEWL and inflammation again. Scratching fires automatically once itch passes 65%, or you can trigger it yourself. Emollients rebuild the lipid mortar (raises B); corticosteroids calm inflammation and speed the decay of scratch damage — together they can break the cycle even without fixing the underlying filaggrin deficiency.

Filaggrin / Humidity — the underlying skin genotype and environment.
Emollient / Corticosteroid — the two mainstay atopic-dermatitis treatments, acting on different parts of the loop.
Scratch now — manually damages the barrier to see the loop accelerate.

Stratum corneum Epidermis / dermis Water vapor (TEWL)

⚠ Couldn't load the 3D engineThree.js failed to load from the CDN. Check your connection and reload.