What do "they" refer to here?

A poorly written sentence Oristar. Much clearer would be

"they" refers to "the thousands of things people do"

when they {the thousands of things that people do} are subjected to scientific study they [the thousands of things people do} don't work

It means:

There are a thousand things out there that people do and when those people are subjected to scientific study, the things that dermatologist thought would work turn out not to.

what doesn't work is the thousand things that people do.

You need "does", not 'do', Oristar.

What does [the word] "they" refer to here?

Isn't English silly?

Was this a report of the doctor's direct speech, Oristar?

I should have mentioned that the meaning here is,

What do ["they"] [= "those people/some people" previously referenced] refer to here?

I don't feel that way, Panzade. I find English, complicated as it is, to be endlessly fascinating.

Got it, thanks.
It is from USA Today's report.

of course you do...and so do I, but you might agree with my sentiments more if you had learned it as a second language, as I did

Wow, whoda ever thought? Im pres sive !

As I've always said, the greatest impediment to the acquisition of a second language is a first language.

That's so very true JTT , but what I always say is: The most effective catalyst for learning a second language is that four ten year-old boys are gonna kick your ass for talking with a Spanish accent.

Can I ask, Panzade, how old were you when you started to learn English?

I was 8 when I started taking English classes at an academy called Toil Y Chat in Buenos Aires. We derisively called it Toilet Chat.
English is a very very difficult language to learn in a classroom, the pronunciation rules alone are so whimsical. I remember coming in second in a spelling bee in 4th grade because I misspelled Wednesday.

I did much better once I was immersed in the American culture. Like you, I think American English is a fascinating language, never more so than on Saturdays when I attempt the NY Times crossword puzzle.

I agree given that many teachers have the imagination of a gnat. If you "teach" a language as it's "taught" to children in any language, that is, not taught but done, and this is vitally important, in as full and as rich a context as is possible in a classroom setting then it isn't difficult.

I've had kids of 6 to 15 playing a simple game of cards, using new to them, realistic native structures in under 15 minutes. They were learning the language in context, eg.

A: Do you have a five?

B: Nope, Unnuh, Naaahh, I don't.

OR

B: Yup, Yeah, Unhuh, I do.

A: Give it to me.

B: Okay, Okiedoki, here you go.

Virtually all simple structures/collocations can be demonstrated so that the language matches the context. Even the subjunctive, though I'm not suggesting that as a starting point.

Children up to 12 or so are masters at pronunciation. All they have to do is hear it enough times, from a competent speaker and they pretty much can't help but get it right.

How long were you immersed in American English and from what ages to what ages?

Were you "taught" that 'could' is the past tense of 'can', 'might' the past of 'may', 'should the past of 'shall', 'would' the past of 'will'?

Were you "taught" that 'could' is the past tense of 'can', 'might' the past of 'may', 'should the past of 'shall', 'would' the past of 'will'?

Panzade, I'll move this to the "Really, modals are tenseless" thread and if you feel so inclined you can reply there.