MI Contact Allergy: Check More Than Your Face Cream

A confirmed methylisothiazolinone allergy calls for checking products beyond face cream. This preservative, often shortened to MI, can occur in personal-care and household products, according to the British Society for Cutaneous Allergy¹.¹

Check bathroom, laundry and decorating products

The society lists these possible sources. Not every product in each category contains MI.¹

Where to check	Examples from the leaflet
Bathroom and changing bag	Soap, shampoo, conditioner, moist toilet paper and baby wipes.
Laundry and kitchen	Washing-up liquid, laundry detergent and fabric softener.
Decorating and hobbies	Household paint, glue, wood stain and children’s slime.

Photograph the front and full ingredient panel of each product you need help checking. Include its exact version and where you use it. A useful note reads “liquid hand soap beside the kitchen sink, used after washing dishes,” rather than “soap.”

The American Academy of Dermatology² asks patients to describe work, hobbies, everyday activities and products applied to someone they care for.² Include a child’s shampoo or a parent’s body lotion if you handle it, even when you do not use it on yourself.

Paint needs a separate question. The allergy society warns that fumes in freshly painted rooms can cause problems and MI may not appear on the tin.¹ Tell the clinic about recent decorating and ask the supplier for ingredient information using the allergen name. Do not treat a missing name on a short label as confirmation that the product is suitable.

Read the related names with your clinician

Methylchloroisothiazolinone, or MCI, is a related preservative. The society advises people with MI allergy to avoid it too; some may also need to avoid octylisothiazolinone.¹ Ask the clinic to mark every name covered by your instructions.

Related preservatives do not produce identical test results in everyone. A North American study reviewed 9,028 patients patch tested during 2017–2020. Of the 1,976 who reacted to at least one tested isothiazolinone, 871, or 44.1%, reacted to more than one. The tested substances included MI, the MCI/MI mixture, benzisothiazolinone and octylisothiazolinone.³

This was a retrospective study of patients undergoing patch testing, with no follow-up data. Those percentages do not estimate allergy in the general population or predict your reaction to another preservative.³ Have the dermatologist interpret your own results and explain whether further testing would change the avoidance plan.

Check replacements against the bottle you buy

If your clinician supplies access to the Contact Allergen Management Program, or CAMP, its product list is linked to your allergen codes. The American Contact Dermatitis Society’s⁴ toolkit still tells patients to compare the ingredients on the actual product with the list: formulations can change. Changes to the allergen codes go through the provider.⁴

Save a photo of the replacement’s ingredient list and the date you started it. If a listed product and its packaging disagree, ask the clinic before using it. An old screenshot of a suitable product is not enough to check a reformulated bottle.

If the rash keeps returning

Take the product record back to the dermatologist and explain what you changed, when, and which areas remain affected. Avoidance and treatment belong in the same review; the AAD advises telling the dermatologist when rashes continue despite treatment.²

The “Your Shelf” section in Skin, Head to Toe discusses a shorter routine and formal patch testing for recurring product reactions. Use that approach to keep the product review manageable, with the clinic’s MI avoidance instructions beside it.