Hi VITI
Considering medical assessment of your allergic reaction and the very small micron pore size, as Jeff suggested, our Expert advisers here (Thank you Jeff! 
) would better assist you in selecting the correct encasement for your situation. In case you must make a selection before you have the chance to find out what you are allergic too and for the benefit of others who have significant allergies then a mattress encasement that completely surrounds the mattress may be worth considering (even though some of them may reduce the ability of the mattress to breathe and ventilate) to protect against dust mite allergens (and/or bed bugs if this is an issue). There is more about mattress encasements in post #2 here and about dust mite allergies in post #2 here.
mattress protectorsThere is a bit more information about mattress encasements (vs ) that are the “allergy” type and are made with a pore size of about 5 - 6 microns or less which prevents most allergens from penetrating the fabric. The most common of these are dust mites which are fairly large on a micron scale but dust mite feces, particles, and larva can be 10 microns or smaller and dander can be 5 - 6 microns or smaller and some other allergens can be smaller yet so the smaller the pore size the more complete the allergy protection ( see here and here for some common allergen sizes). For most people 5 - 6 microns will be enough to prevent most allergens. These are available in natural fabrics such as cotton which are usually in the 4 - 6 micron range and made so that the pore sizes stay consistent with washing. An example of a cotton blend is the Allersoft here and 100% cotton is here . There are also many others that use synthetic fibers ( such as here ) where the pore sizes are smaller yet which may offer more complete protection for smaller particles but may not be as effective for ventilation or at absorbing and wicking away moisture (which is part of temperature control) which is why natural fibers tend to sleep cooler than synthetic fibers (which don’t absorb moisture). Rayon type “semi-synthetic” fibers that are made from cellulosic materials such as bamboo, wood, or eucalyptus also absorb moisture and are similar to natural fibers in their ability to absorb and wick moisture. Some information about various allergy mattress encasements is here and there are also some comparisons of micron sizes between several common brands here.
I’ll be interesting in finding out what your findings are about your symptoms and what you decide to do.
Phoenix