2-Mercaptobenzothiazole
The rubber chemical behind most "shoe dermatitis" — the foot rash that antifungal cream never fixes
INCI2-Mercaptobenzothiazole
- Category
- Rubber_accelerator
- Risk level
- medium
- Top shoe allergen
- MBT is one of the most frequently identified causes of shoe contact dermatitis in global patch-test databases
- Two jobs, two exposures
- Used as a rubber accelerator (shoes, gloves) and as a biocide/corrosion inhibitor in metalworking and cooling fluids — so both consumers and industrial workers meet it
- The look-alike trap
- Bilateral foot dermatitis is often treated as athlete's foot for months before shoe allergy is considered
- Cross-reacts with
- Other benzothiazoles, including MBTS (formed when MBT oxidises)
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This ingredient may appear under any of these names:
Commonly found in
Possible reactions
- Bilateral, symmetrical rash on the tops of the feet and toes
- Foot dermatitis that worsens in hot weather
- A foot rash that doesn't respond to antifungal cream
- Hand dermatitis from rubber-handled equipment (occupational)
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What is 2-mercaptobenzothiazole?
2-Mercaptobenzothiazole (MBT; trade name Captax) is a sulphur-containing ring compound that does two jobs. In rubber manufacturing it's a vulcanisation accelerator, helping cross-link rubber during production. In industry it's a biocide and corrosion inhibitor, added to metalworking fluids and cooling-system water. Those two roles create two completely different exposure routes — one through everyday shoes, one through industrial work.
MBT belongs to the benzothiazole class, chemically distinct from thiurams and carbamates, and it's a fixture of shoe-dermatitis patch-test panels. Its claim to fame is shoe contact dermatitis: rubber chemicals in soles, insoles and shoe adhesives leach through to the foot, especially under hot, sweaty, occluded conditions.
Why it causes reactions
MBT carries a reactive thiol (–SH) group that forms disulfide bonds with skin proteins, creating the hapten-protein conjugates that drive Type IV delayed hypersensitivity. A few features define the clinical picture:
- A shoe-shaped rash. Classically a bilateral, symmetrical dermatitis on the dorsum of the feet and toes — wherever the shoe presses — sometimes spreading to the soles.
- Summer flares. Sweating accelerates leaching, so the rash worsens in heat and improves in open footwear.
- An occupational route too. Metalworking and automotive workers can meet MBT in cooling/cutting fluids, a hand-and-forearm exposure quite separate from shoes.
This is one of those allergens that hides in plain sight. People assume a stubborn foot rash must be a fungus, buy more antifungal cream, and stay stuck for months. The pattern is the giveaway: a fungus tends to start between the toes, a shoe allergy mirrors the shoe. If antifungals aren't working and the rash matches your shoe, that mismatch is the clue worth chasing. — Snehal
Where it's found
Consumer products
- Rubber-soled shoes — the big one; present in outsoles and insoles.
- Athletic footwear — trainers and sports shoes with significant rubber.
- Rubber-based shoe adhesives used in construction of the shoe.
Industrial / occupational
- Metalworking coolant and cutting fluids (corrosion inhibitor).
- Cooling-tower water treatment (biocide).
- Rubber-industry manufacturing.
How to spot it
Because MBT isn't on any consumer label, you identify it by pattern and test:
- Note a bilateral, symmetrical foot rash that tracks the shoe.
- Watch for improvement in sandals or barefoot, and worsening in closed shoes.
- Confirm with patch testing at a contact-dermatitis clinic — ideally including a sample of the actual shoe material.
Safer alternatives
- Leather or polyurethane soles — far less rubber contact than rubber soles.
- Open leather sandals, especially in warm months, to cut contact and sweat.
- Cotton socks as a barrier between shoe rubber and skin.
- Footwear certified rubber-accelerator-free where available.
The bottom line
2-Mercaptobenzothiazole is the rubber chemical behind much of the world's shoe dermatitis — a symmetrical, shoe-shaped foot rash that flares in heat and shrugs off antifungal cream. If that description fits your feet, think shoes, not fungus: switch to leather or PU soles, try open footwear in summer, and patch test to confirm.
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