Worst medical fallacy?

[thikasabrik]

Apart from the obvious one about solitary activities making you go blind, what's the worst fallacy you have come across? Mine dates back to the 1960's when I hit puberty and a very elderly relative told me never to wash my hair if I had a period. When I asked her why, she said "It could prove fatal."

[tetherend]

An elderly relative was told in the 1950's that to help to cure his arthritis he should have his ears pierced.  He had his ears pierced and it made no difference whatsoever.

[spainlads]

I'm circumcised and was told that I only had one tecticle has the other one of the 'red end' on show. I was convinced I'd grow another one :)

[OBonio]

A doctor told my wife not to worry about her small bleed during pregnancy. A 2nd opinion had a VERY different view as she is rhesus neg and I'm rhesus pos.... could have seriously harmed the baby. Cheers then doc!

[Guinevere]

Hi thikasabrik - I heard that one as recently as the 90s!  There's also the one about not having a bath when you have a period. 
I'm quite interested in where all these come from.  Maybe the ones about periods stem from the days when meat was a bit more scarce in one's diet, therefore having a period could lead to anemia/lowering of immune system, and getting wet (bath or hair wash) would mean getting cold and therefore upping the chances of catching something/dropping dead.
Just a theory....
I have also heard some mind-boggling ones about how not to get pregnant (having sex standing up, in a swimming pool, not being able to get pregnant when it's your first time, getting rid of an unwanted pregnancy by sitting in a hot bath drinking whiskey! Etc!)
I kid you not, and they were still doing the rounds when I was a teenager (in the 90s!)

[kaktus]

One of the most harmful, must be the myth that HIV/AIDS is cured by having sex with a virgin! Of course a lie, but with terrible consequences.

On a lighter note, my dad was told that if he just ate a apple before going to bed, he wouldn't have to brush his teeth.

[Hermia]

My gran claimed she had a "floating kidney" (her kidney floated around her body making her ill)!

[judypark]

As a trained nurse I get to hear plenty from elderly patients, feed a cold, starve a fever is absolutely asking for trouble. Also my mother always told me never to sit on a cold surface as it would give me piles, interestingly the treatment for piles is to shrink them by freezing. Another favourite on a uncomfortably hot ward at 85 degrees when you try to open a window, the elderly will complain that they will "catch their death" from a draft! Actually fresh air has never killed anybody yet, however stale static air carries bacteria and viruses. Hey Ho. Judy

[judypark]

Hermia,  when I was at Uni we had a lecture about the history of med. terms. The Romans believed that womens' uteri floated  about their bodies and caused madness or hysteria, it was known as a "wandering uterus" Hence the term hysterectomy. Fortunately for todays surgeons, the uterus seems to have permanantly migrated to a predictable location. Good news for us ladies. Judy