My daughter's boyfriend is also cat-allergic, and we've found things that can help:
1. I use an air-conditioner filter that is good for pet dander. The 3M brand can be found at Walmart, Target, Home Depot and most grocery stores.
2. A vacuum cleaner with a HEPA filter can also help. I've got a Dyson Animal, and it works wonders.
3. Steam cleaning can help too, even on the water-only setting.
4. There are also dander-reduction products that can be applied to the cat, usually weekly. Many pet-supply stores carry them.
5. Make sure any furniture slipcovers are washable, and do it regularly.
I don't do #4, but everything else seems to work well. The boyfriend can handle being in my house with several cats now.
Also, thank your son for trying to work with the cat situation. So many people will dump a cat quickly when such a thing happens.
