What is so special about these particular cats is that they are naturally hypoallergenic - at least to some extent.
There are 5 main allergens associated with cat allergies. Of these, the main offenders are glycoprotein Fel d1 (from the cat’s sebaceous glands or sweat glands) and Fel d4 (from cat saliva). It appears that the majority of people who are allergic to cats are allergic to one or both of these 2 allergens.
There are 2 breeds of cat that naturally make much less of these two allergens than most cats. They are the Siberian and the Russian Blue.
Although there is not a large amount of published data, it appears that the majority of people who are allergic to cats do not react to Russian Blues. We have seen this in our family and friends. The only way to test any individual is by visiting with a Russian Blue.