Fragrance sensitivity

[Sly Saint]

The Dangerous Myth of "Hypoallergenic" and "Green" Products
Because general literature positions "natural" or "eco-friendly" as synonymous with "safe," consumers are led to believe they are at zero risk. In reality, because isothiazolinones are highly effective biodegradable biocides, they became the go-to preservative for "green" or "plant-based" brands looking to avoid parabens. A consumer trying to find gentle products for their family is often unknowingly exposing themselves to maximum-strength sensitizing agents. https://link.springer.com/article/10.1684/ejd.2016.2951

Why This Matters for the Un-Sensitized
Every single time a person with perfectly healthy skin washes their hands with a MIT or BIT-preserved washing up liquid, or sleeps on sheets washed in an MI-preserved detergent, they are playing Russian roulette with their immune system. If their skin barrier is even slightly compromised (due to dry winter weather, a small scratch, or mild shaving irritation), these potent chemicals can slip past the epidermis and sensitize the immune system permanently. https://dermnetnz.org/topics/isothiazolinone-mix-allergy

 

[MeSci]

Oh well, I've used it for many years and never had a problem.

Maybe they just list possible problems for legal reasons.

 

[Sly Saint]

My reactions are systemic, mast cell activation symptoms, especially to airborne MI from decorating paints/products and cleaning products, rather than the more common dermatological ones.

I've just re-read your post.
What you call 'systemic', this is an allergic reaction , when someone has become sensitised to the allergen and can produce widespread skin reactions. This is in addition to possible respiratory problems if inhaling airborne particles.

Unlike "Irritant contact dermatitis" where the reaction is only where the product has contact with the skin, Allergic contact dermatitis from these chemicals more often than not produces a systemic reaction, and often areas that have not come into contact with the allergen are also affected.

So both are systemic. You are "lucky" not to have any skin reaction. I have no idea where "Mast cell activation" comes into it.

Allergic reactions to MI typically appear as red, raised patches on the skin that can progress to blisters, crusting, and even ulceration in severe cases. The reaction isn’t limited to the area where a product was applied. In one clinical study of 23 patients with confirmed MI allergy, 90% had rashes that spread beyond the original contact site, with the legs affected in 90% of cases

What Is Methylisothiazolinone Used For and Is It Safe?

Methylisothiazolinone keeps products fresh, but it’s also a common cause of skin allergies. Here’s what you need to know about MI and how to spot it.

scienceinsights.org

.. allergies to these chemicals are becoming increasingly prevalent

problem is most people won't know that these chemicals are causing the problem. They might identify a particular product, but not pinpoint the exact ingredient because these ingredients do not have to be disclosed in listings.