There will be millions of people in Britain who can sympathise with the plight of the US President-elect, Barack Obama. Not the huge challenges he faces as leader of the free world, but the task of finding a hypoallergenic puppy for his daughter. While it may seem frivolous to the lucky allergy-free, the misery of pet-induced reactions is all too familiar to many.

The first challenge is that allergic reactions are intensely personal; no one responds in exactly the same way. This is because the symptoms are not caused by the allergen, but by the body's reaction to it. The immune system of an allergic person sees the harmless dog hair or rabbit fluff as a dangerous invader.

Or, more accurately, it misidentifies proteins on the animal hair or dander (dried skin), as potential infections. Its response is to produce an over-the-top defence reaction, releasing a cocktail of potent chemicals that cause inflammation. And it is this inflammation that leads to everything from itchy eyes to lethal anaphylactic shock.

So while some people must avoid alsatians, others must dodge daschunds. It is how your body responds to different animals that counts; something almost impossible to predict. You won't know for sure until you try.

The commonest allergies

Dog and cat allergies are the most common, probably because they are the most popular pets. And the majority of allergies are to proteins produced in glands on the animal skin and in the saliva. Called Can f1 in dogs and Fel d1 in cats, they coat the fur and are shed in the animals' wake. These proteins are similar, which is why some people are allergic to cats and dogs.

However, they are not the only culprits. Other proteins, such as Can f2 or albumin, can also trigger an allergic response. And then there are those proteins produced by other animals. Allergies have been recorded to rabbits, cows, horses, guinea-pigs, mice and rats.

It's not possible to tell exactly which bit of your pet you're allergic to without detailed tests. Some private clinics and laboratories offer these tests, but beware: the field of allergen testing is full of spurious, unproven methods. Some sound very scientific, such as cytotoxic or electro-dermal testing. However, they have no research evidence to back them up and they can be expensive.

If you are interested in being tested, your first stop should be your doctor. Don't forget that knowing what you react to may not help you to choose the right dog because all dogs produce these proteins and there is no such thing as a truly non-allergenic dog. Obama's quest is going to be tricky.

Hypoallergenic breeds are ones that simply produce fewer proteins and so, hopefully, do not produce such a strong reaction. The same goes for cats, guinea-pigs, rabbits, etc. There are even some suggestions that individual animals produce different amounts of allergens. So replacing your favourite pet with another of the same breed may not always do the trick.

There are, though, a number of things you can do to ease pet allergies, and there is even the prospect of genetically-engineered allergen- free pets in the future.

Choose your breed carefully

Some dogs seem to produce fewer reactions for a number of possible reasons. They may shed less hair, shed less dander or have lower amounts of the allergens. There are lists of hypoallergenic dogs, such as poodles or schnauzers, published by a number of organisations; the Kennel Club's list of low-shedding dogs can be found at http://www.thekennelclub.org.uk/item/2100. Similarly Rex and naked Sphinx cats are reported to be hypoallergenic.

Washing your pet regularly can also help as it removes much of the hair, dander and allergen, preventing them from getting into the air. (Good luck with bathing your cat, by the way.) People with rabbit or guinea-pig allergies should keep their cages spotless as it tends to be the animals' urine that contains the allergens.

Remember that your reaction is individual and while these animals are a reasonable place to start, it's a good idea to try before you buy. Try to visit your potential pet before you commit to see how you respond. Many people get a reaction within seconds of coming into contact with an animal, though it can take much longer. If you really struggle, reptiles and amphibians rarely cause problems.

Keep your house - and your hands - clean

Regular vacuuming with a cleaner equipped with a HEPA filter (which retains 99 per cent of the dust hoovered up) can help to reduce the amount of allergen in the house. It might also be worth keeping a scrupulously pet-free room, the bedroom being the best bet. And wash your hands thoroughly after touching a pet.

Genetically-engineered animals

Modern genetic engineering can, in theory, produce a pet that is totally free of any particular protein. So far, attempts to genetically engineer cats free of Fel d1 have failed. However, as the technology improves, truly allergen-free pets may well arrive.

The closest science has got to date are the hypoallergenic cats offered by the US company Allerca (www.allerca.com); for hypoallergenic dogs visit www.lifestylepets.com. These animals have been bred conventionally to have low levels of the main allergens. But they come at a price, from $7950 (about £5,300). Animals imported from the US to the UK under the Pet Travel Scheme have to be vaccinated against rabies. For more details visit www.defra.gov.uk.

Talk to your doctor about a drug regimen

There are many antihistamines available over the counter to reduce the effects of allergic reactions. And just as everyone's response to allergens is unique, finding the right treatment is a matter of working out what's best for you.

Build a tolerance

People can develop tolerances to allergens and many sufferers build up a natural tolerance to their pets. This is exploited in a treatment called desensitisation. Small amounts of the allergen are given over a few weeks, normally by injection just under the skin. It is most commonly used for hay fever, and only rarely for pet allergies, in the UK. Such treatments must always be carried out under strict medical supervision as it could produce an unexpectedly severe immune response. Always ask your GP.

Times recommends

• Are eldest children really a cut above?
• Peaches Geldof: censored
• Top 10 style-setting films of all time