British Society of Cutaneous Allergy (BCSA)

Methylchloroisothiazolinone (MCI)

What are the aims of this patient information leaflet?

This leaflet has been written to help you understand more about your contact allergy. It tells you what a contact allergy is, what causes this allergy and what you can do about it.

What is contact allergy?

Dermatitis, also known as eczema, describes a type of inflammation of the skin. Contact dermatitis or contact eczema is a term used when this inflammation is caused by direct or indirect skin contact with something in your environment. Allergic contact dermatitis occurs when your immune system causes allergy to a very specific chemical or substance that has been in contact with the skin.

What causes your specific allergy?

Your patch tests indicate that you have a contact allergy to methylchloroisothiazolinone.

What is methylchloroisothiazolinone?

Methylchloroisothiazolinone (MCI) is a preservative used in the manufacture of water-based cosmetics and personal care products. Other names for methylchloroisothiazolinone include Kathon, Euxyl K 100 and Grotan K.

What are some products that contain methylchloroisothiazolinone?


  • Soap
  • Moist toilet papers, wet wipes or baby wipes
  • Shampoos and conditioners
  • Hair products
  • Skin cream and body lotions
  • Bubble bath and shower gel
  • Mouthwashes
  • Sunscreens.


  • Detergents and washing up liquid
  • Fabric softener
  • Ironing water
  • Glues
  • Polishes
  • Water-colours and household paints (Note: paint fumes can cause problems in freshly painted rooms and methylchloroisothiazolinone may not be labelled on the tin).


  • Car polish and windscreen products
  • Glues and adhesives
  • Cutting oils and coolants
  • Biocides.

Methylisothiazolinone is a preservative which was banned from leave on cosmetic products in 2017 and restricted to low levels in wash off cosmetic products in the EU.

Remember, always check the label, these lists can never be complete and ingredients change.

How can I manage my allergy?

This means that you should avoid putting products containing methylchloroisothiazolinone onto your skin in the future.

You may also need to avoid octylisothiazolinone containing products.

Self-care (what can I do?)

Always check the ingredient listing on the product, package or package insert as these lists can never be complete and ingredients change. This is particularly important for any products purchased outside the EU where some allergens may not be banned.

Created: 2015