|Hi Maggie -
This is one time I'll have to say that your doctor was quite wrong about the clothing. If you look at the chemistry, it's easy to understand why he's wrong but you can't fault him. I've read others say the same thing - that the clothes are permanently contaminated. Let's look at this with some logic and see why there is fault in his statements.
Poison ivy has a secondary compound called urushiol oil which is the compound which causes the rash. This heavy oil resides in resin canals within the plant's leaflets, stems, vine, fruit, and roots. Only upon injury to the plant is the oil released but unfortunately for us, the plant is quite fragile. Urushiol oil is quite stable and will "stick" to any surface including our skin, pet fur, tools, clothing, etc. Urushiol oil can remain on surfaces for some time. There have been reported cases of contact dermatitis from urushiol oil on items hundreds of years old. Urushiol oil may remain on a surface only a few months or many years so a number of just 1 year is not an accurate statement. Environmental conditions will determine how long the urushiol oil will remain potent.
But in the end, we are still talking about an oil. Oils can be removed using soaps (including detergents), solvents, or other oils (remember like dissolves like). The key will always be to use enough water or liquid to remove the urushiol oil completely from the surface. Soaps work by attaching one end to the oil and the other to water which can then be removed. Please see How Soap Works for more details. Solvents work by placing the oil in solution - again the key here is to then remove that solution by using enough solvent or using water (itself a type of solvent). Not all solvents work the same so you need to use an appropriate solvent to remove the oil. Urushiol oil is soluble in alcohol, ether, or benzene. Apparently, you can also use baby oil as it works on the principle of "like dissolves like". An oil will dissolve an oil.
So based on the chemistry we see that washing the clothes with a detergent will be sufficient to remove the urushiol oil. There are a few caveats of course - 1) don't overfill your machine or use too little water and 2) use a detergent, solvent, or other product designed to remove dirt, grease, oil. You must be careful in placing the clothes into the machine as you could accidently contaminate the outside of the machine with urushiol oil by having the clothing brush up against the sides. I always set my machine at the highest setting for water level, use a long wash cycle, and use the manufacturer's recommended amount of detergent.
Now the last problem I have with the doctor's statement - burning the clothes. Burning items with urushiol oil on them is a definite no-no. Urushiol oil is fairly stable and can become airborne on dust or smoke particles. Inhaling urushiol oil is far worse than just ordinary contact with the oil. In fact, 1/3 of firefighters who battle forest blazes in the west develop rashes or lung irritations from airborne urushiol oil.
I have quite a few more references it you'd like them. Burning the clothes is not only unnecessary but can also be hazardous. Urushiol oil is a well understood chemical compound that can be removed from surfaces provided you follow recommended steps.
Just a few of the references used for this response: