No, Sphynx cats are not hypoallergenic. Sphynx cats are like any other domestic cat in that they have the Fel D1 allergen in their saliva which like any other domestic cat they deposit on their skin rather than on their fur. Although it should be said that they have a very fine down fur coat which you can’t see but which can be pigmented. I believe that there will be variability as to the allergic properties of Sphynx cats (see below).
Sphynx cats groom themselves and the saliva deposited on their skin is added to the oil already there, secreted by their sebaceous glands inside their skin, which leaves, I’m told, a sticky sometimes crusty residue of oil, sweat and spit on their skin. That sounds unpleasant but it means that dried saliva containing the allergen ends up in the home causing an allergic reaction to someone predisposed to an immune reaction to this allergen (10% of people are).
The problem is that some websites say that Sphynx cats are hypoallergenic because they don’t have fur but I can’t see the argument in that statement. The argument is not whether they have fur but whether they produce the allergen in their saliva. And Sphynx cats are perfectly normal domestic cats except for the fact that they are more or less hairless. They do have this allergen in their saliva and therefore they cannot be hypoallergenic. Note: hypoallergenic means less likely to produce an allergic reaction. It does not mean no allergic reaction.
Individual cat variability
That said, some individual cats are probably going to be less of a problem than other individual cats with respect to the Fel D1 allergen. I think that it is more sensible to test domestic cats on an individual cat basis to see whether one of them is more hypoallergenic than another. I believe that it’s unwise to decide whether a cat is hypoallergenic or not based on their breed. That doesn’t really work in my book.
There’s lots of discussion on the Internet about hypoallergenic cat breeds which I think is a waste of time, except perhaps for the Siberian which may have hypoallergenic properties but I wouldn’t guarantee it. Despite the breed being promoted as being hypoallergenic the information is anecdotal and unsupported by hard science. It may be that some individial Siberian cats are genuinely hypoallergenic as are some individual cats of other breeds and random bred cats.
Variability among people too
If a cat produces the Fel D1 allergen, and all of them do to varying amounts, then a person can be allergic to them. There is variability among people too as to how allergic they are to domestic cats. And sometimes an allergy to a domestic cat can ease over time. This variability is important because it means you shouldn’t necessarily write off having a domestic cat. There are ways around the problem. An injection is being developed to cure people allergic to cats!