[Rankenstein]

I can't say exactly why this has happened but using your acne-scar.html page (and the other acne pages) as an example, it looks like you have gone too far with the SEO.

That page has a lot of useful information, no doubt there, but there is a bit of spammy stuff there too, e.g:

"The best thing to remove acne scar is to get an acne scar product. However, before you buy any acne scar products such as acne scar creams and scrubs, remember, acne scars do not go away overnight. It takes at least couple of months for removing acne scars completely. No acne scar product or acne scar cream can magically remove your acne scars in a day or two.
Therefore, beware of fake acne scar products and acne scar creams which misguidedly claim to remove your acne scars within no time.
If you want to remove acne and acne scar, get all the facts right and myths cleared."

As I say, you have good info on your pages, but it is somewhat spammy like the above, much too much keyword density IMO, and there are other things which stand out: The acne scar treatment and acne scarring treatment pages are the same thing, so you can definitely call that spammy. In fact, they are classic doorway pages that search engines don't like. Take one down and 301 the other to the one you want to keep.

I hope you understand, I'm not trying to cause you trouble. The site is informative, that's a great basis to work from, but you've gone really over the top on the SEO. That's what I think might have caused your problem.

Also you've put too many links to other internal pages in the page content. You only get credit from Google for the anchor text of the first link to a page that it finds so it's pointless repeating it anyway.

Well, that's my opinion about it.