Though thought to be hypoallergenic, NO cat is completely allergy free. Cat specific allergies are caused by the protein Fel D1 which is primarily found in the cat's saliva. The cat licks itself transferring the protein to it's coat, which then is transferred to carpet, clothing, and to humans. Though the Sphynx is virtually (not completely) hairless and does not shed, it is still a cat and still licks itself to groom. With that, it is possible that a Sphynx is more "tolerable" to suferers than most other cats. My husband has asthma and allergies that are triggered by the traditional cat, yet our cats are able to come into close contact with my husband (even in his face) and he has no issues.
Though the Sphynx has little fur, they are not maintenance free. Due to their lack of coat, body oils that would normally be absorbed by the coat of other breeds builds up on the skin. They need bathing on a weekly basis which should include cleaning of the ears and trimming of the nails. Care should be taken to limit the exposure to the outdoors, as the Sphynx is susceptible to cold (freezing) and heat (sunburns, sunstroke, and/or skin cancer). Due to their higher metabolism, Sphynx cats need a diet that is high in protein. This does not have to be expensive, just read the labels; the higher the protein, the better.
The lifespan of a Sphynx can be up to 15 years. Sphynx are known to have instances with the genetic disorder Hypertrophic Cardiomyppathy (HCM), thickening of the heart muscles. Yearly scans can help manage the genetic "passing on" of HCM. A key point to remember, just because one scan is negative does not indication that your cat is "safe." HCM can occur at any age, and there is never a guarantee that your cat will always remain HCM free. (For further information, please see the HCM FAQ tab).