How did the sweatdrop originate?


I can kind of handwave or fanwank the origin of things like the exasperated
faceplant or the vein popping out when a character is comedic-angry, and even
the trope of Japanese flag fans coming out when people want to cheer on their
comrades, but how did the sweatdrop come to characterize the feeling of sort
of embarrassed contrition?

![An image showing the sweatdrop in Fullmetal
Alchemist](https://i.stack.imgur.com/2wu7k.jpg)

I can't come up with anything logical just based on speculation. Is this an
outgrowth of the [_manzai_](http://en.wikipedia.org/wiki/Manzai) tradition,
with the
[_tsukkomi_](http://en.wikipedia.org/wiki/Glossary_of_owarai_terms#tsukkomi)
and [_boke_](http://en.wikipedia.org/wiki/Glossary_of_owarai_terms#boke)
characters?




There doesn't seem to be any "official" announcement for that, but I think
it's safe to say that since Manga and Anime make heavy use of symbols to re-
create a concept or a situation, the sweatdrop functions the same way. In
other words **sweatdrop** (see image below) is a reference to the fact that
when people feel uneasy or feel similar emotions, they usually get sweaty. You
don't get _that_ sweaty in real life, but again, they're symbols.

More symbols that might prove this point:

  * The **cruciform popping veins** are a clear reference to the veins that pop out and can be seen pulsating when you're _nervous_ or you're about to lose it.

![enter image description here](https://i.stack.imgur.com/1MMlZ.png)
[Source](http://upload.wikimedia.org/wikipedia/commons/thumb/7/71/Anirage-
alternate.svg/200px-Anirage-alternate.svg.png)

  * The **red cheeks** when you're embarrassed (blood flowing), the **red nose** when you're drunk (yes, nose has that tendency sometimes when you get drunk).

  * The **saliva drop** when you're hungry. Your mouth does get watery in that situation, because it anticipates the food you're about to eat. Mastication is the first stage of digestion.

  * The eyes shaped like **>. <** that indicate nervousness or excitement. (I bet everybody can picture this face expression).

And so on. There is more (as a start) on the Wikipedia page for [Manga
Iconography](http://en.wikipedia.org/wiki/Manga_iconography).

