This started for my spouse’s dermatographism after testing positive to almost all environmental triggers (dust mite, pollen, mold, cat and dog, etc.). This may all be due to mast cell activation syndrome (MCAS). In real life my partner reacts to dust mite, some pollens, cats, and possibly mold.
No fragrance (soaps, shampoos, laundry detergent, lotion, cosmetics, etc.).
No harsh cleaners (vinegar, baking soda suffice for most jobs).
Hot wash and dry all sheets, pillow covers, blanket covers, etc. at least once every two weeks. Dust mite reproduce in a month.
Use a dust mite proof mattress cover.
On a side note, it may actually help to NOT make your bed. Dust mite thrive in moist, warm environments. Expose your bed to the cool and dry air. Hang blanket over headboard or something if possible.
No carpets, if possible.
Vacuum frequently (at least once a week) with a model that has hepa filters.
Ventilate. Ventilate. Ventilate. Keep everything dry.
Keep an eye out for any spots that tends to hold moisture for mold growth.
Treat with vinegar at first sight of any mold.
Be very careful about using chemical insecticide, try to find alternatives. Diatomaceous earth maybe?