We have all heard the admonishment. Was there ever a scourge of dirt behind children’s ears? I never scrub my back, and have never developed a malignant fungus there, either! What is the purpose of this warning?
Beacuse sweat makes that place stink real bad ! We do tend to forget to clean behind the ears, especially kids .
Yeah, you never know what’s gonna grow there.
White heads, black heads.
Never heard that. If you wash your hair, don’t you automatically wash behind the ears? My feeling is that it is just one of those things parents say. Why would it stink behind your ears? I can think of lots of other places that might stink worse. “Be sure to wash underneath your balls” or “soap up your asshole” comes to mind. 
My supposition is it is just a cute way of saying “clean yourself thoroughly” without getting too scatological.
In my case, the sweat flowing down from my hair on back of head does make it stink if left uncleaned, whenver I touch there and smell it.
I wash it automatically once I beame a teen. Before that my parents had to tell me.
It kind of gets oily from sweat and oils from your hair. I usually get it while washing my face and hair.
Potatos, if my old mum is to be believed.
But when parents said this (or at least when they started saying this), kids washed their faces daily but only had their hair washed maybe once a week. So parents were admonishing kids to wash behind their ears daily, as well, rather than wait for the Saturday night hairwash.
Kids played and got a lot dirtier in general in the past. None of this staying in a clean room and playing computer games. Everyday was a physical work and play day. The families had 5 or more kids and they cleaned up without individual attention from the parents. Mom would give them a short inspection of hard to clean places to see if they washed up or just did a quick rinse off. Wash behind the ears was often yelled so they didn’t have to send them back, because they had dirty ears. Shampooing wasn’t a daily part of the bath. The kids had a washcloth in the bathtub to clean up. Because of the plumbing and heating the water when my mother was a kid, the family of nine, got to clean up with only two tub fillings. All the boys slept in beds in a barracks fashion.
If you type in the phrase wash behind your ears into a Google Book search, and limit the results to 1700-1900, you get three readable texts. Each concerns a bit of “folk wisdom” or superstition which suggested that washing behind the ears would prevent toothache or other pains/aches.
So, it just might have been a carry over from early superstition.
I found that paying close attention to washing behind my ears with soap, as opposed to just figuring shampoo would take care of it, was very helpful in reducing acne along the jawline.
And she is! It takes but a little soil to root a potato if covered with mulch (substitute hair in this case).
Kids wash only the parts visible to them, and that’s under duress.
I remember reading something to the effect that the warm air generated by the upper body exits through the shirt collar (taking microscopic flakes of skin and other goodies with it) and hits the back of the ears, thus making that area an excellent bacterial breeding ground. (I guess the same might apply to under the chin, but we’re more likely to include that, at least peripherally, in face-washing. Also, as mentioned by other posters, the back of the ears is in close proximity to the hair, which adds oils, dandruff, etc., to the mix.) But I have no cite.
TMI warning…
When my oldest daughter was about three (she’s now 27) she started complaining that her ears hurt. We looked behind her ears and-- EEWWW!!! - there was actually some kind of infected abscess there. We rushed her to the doctor who took a look and backed away briefly with his own EEWWW!!! response before starting to work on it.
Then, of course, he lectured us about cleaning behind her ears. You’d better believe that we paid religious attention to washing thoroughly behind the ears after that.
Bed Bath & Beyond will sell you a really nice back brush, or just have your SO do it for you. I love me a good back scrubbin’.
If I fail to do so, I will wind up with the occasional zit.
As I recall, the area behind the ears is especially rich in oil producing glands (sebaceous glands). These glands are also abundant in the groin, the perianal area, the chest - getting more numerous the closer one gets to the areola - creases of the nose, the forehead and so forth. If we don’t wash, the oils and waxes can build up, and become more visible.
Besides having a lubricating quality, they are responsible for some of the body odors that we have largely rejected in our modern pursuit of cleanliness. They are also responsible for some of the cysts that we may get.
Rub your finger behind your ears after exercise and you will experience a bit of that odor.
I expect that it is normally a good idea to wash off these oils, at least if one wants to keep a job and find a mate in today’s world.
My 2 cents…
I don’t think I’ve ever deliberately cleaned behind my ears, just like I don’t scrub the side of my neck. I always thought it was an odd phrase. I could understand cleaning the inside of the ear, since there are all sorts of nooks and crannies there. Granted, I stand with the back of my head to the blasting shower nozzle, so anything that would stick back there probably gets removed pretty quickly. Do people have folds of skin back there or something. Maybe my ears stick out funny.
It’s not just the oils. Roughly half of us have a fungus back there that smells like melons or squash. If you have it, you probably can’t get rid of it, but regular washing will keep it from getting too ripe.