First things first: there is NO hypoallergenic cat in the world.
Having said this, first we have to understand what is producing the allergy to understand why is the siberian cat, though its semi-long hair, the closest to an hypoallergenic cat.
There are different types of cat allergies out there, recognized up to 8 allergens that cause allergy (Fel d1 to Fel d8). The most important fact is, though, that Fel d1 is responsible of 95% of the allergy cases, so, reducing the Fel d1 exposure will dramatically reduce or even eliminate the allergy reactions.
Another common mistake in the understanding of the allergy is that Fel d1 allergen is in the hair of the cat. But truth is, the Fel d1 protein is present in the skin, the lacrimal, the perianal glands and the cat’s saliva. This means, having a cat without hair, will for sure reduce the exposure as the cats are licking their hair several times throughout the day but it will not eliminate the risk completely.
Additionally, studies demonstrate that neutered cats are producing less Fel d1 protein, so, as a pet, the Siberian is the way to go for most allergics to cats.
Why is the Siberian so famous for allergic people?
The answer is very simple: because of the ridiculously low levels of Fel d1 protein compared with other breeds.
My own experience
All in all, I would like to give you my own experience. I am allergic to cats, as simple as that. I have always suffered with the cats my girlfriend or my family were owning. After some exposure time, I was suffering from the typical allergic reactions, including breathing difficulty. So, I would say my reaction to the allergens was not light at all.
And look at me now, I live with several of these Siberian cats in my own home without ANY problem. And believe me, I am the first interested in having cats that do not produce high levels of Fel d1.
Nevertheless, I will always recommend an hour exposure to see how you feel.