Sulfates in pre-washed salad?

It's probably sodium lauryl sulfate (SLS), which is found in a lot of household products (as well as industrial products) like soap, toothpaste, shampoo, cosmetics, shaving foam, etc. There's some controversy (more of an urban myth) about it being carcinogenic but has been debunked. It is a skin irritant (like most detergents) depending on concentration and duration of exposure. In Europe and the US, SLS is listed as an skin irritant, not a carcinogen. It's in A LOT of stuff that we use.

It is likely the sulfate (in whichever iteration it might be) is a surfactant (similar to soap) used to remove dirty and stuff that water alone would not be able to remove. SLS is a really good degreaser and emulsifier which is why it is in a lot of household and industrial cleaning products. Used as instructed, it's perfectly safe. This is only my educated guess (BS in Chemistry, 8 years R&D experience). Commercial salad producers are a bit tight lipped about how their salads are 'triple washed', so I don't know how other countries wash their packaged vegetables. Likely a proprietary process that they would rather not share with competitors. This may also be the reason why you are having a hard time finding information specifically about this.

Don't confuse sulfates with sulfites. Two different compounds. There's no indication that you need to avoid sulfates or sulfur if you have a sulfite allergy.

In whatever form you decide to buy your salad, learn the proper washing techniques. Sounds silly but it's eye-opening what we currently do that is not really safe.

I haven't heard of that and I'm allergic to sulfites, the chemical they used to use to preserve lettuce. I don't think they're allowed use it anymore. I occasionally use pre-washed salad without getting sick.

Thanks for the replies ! I knew about some of the other issues (although not all mentioned here). Yes, it seems it's best to stay away, but sometimes life demands a few hacks for the busier weeks !

I don't know about sulfates in pre-washed lettuce greens, but I did some research a while back on them in general and found them undesirable for several reasons. Not sure that this applies globally, but worth checking:
1) often already 2 weeks old by the time they reach your grocery store
2) use of chlorine and lots of water to wash them (so there might be an undesirable taste, waste of water resources)
3) they often are dirty (carry bacteria, etc)...so not really very clean after all.
4) they usually cost more than plain, naked greens.

In light of all this, I avoid buying them as no bargain and likely not safe or good quality to eat.
Hope this helps.