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1.
An ingredient in many foods and drinks, most popularly known to be in Mountain Dew, but can also be found in tic-tacs.

An Urban Myth states that this shrinks your testicles.

Not to be confused with Maroon 5.
Samantha: "Why are you drinking that Mountain Dew, don't you know it has Yellow 5 in it?"
Andrew: "Do you honestly think they would sell a product that shrinks your testicles and not even put a warning label on it, or even sell something like that at all?"
Samantha: "Oh... I never thought of it that way"
by Brass Monkey April 21, 2005
 
2.
tartrazine, a synthetic, yellow dye used in many food products and attributed to hyperactivity in children
Yellow 5 is used in mountain dew so much that it led to the development of an urban legend about it causing the testicals to shrink.
by Light Joker January 01, 2006
 
3.
food coloring that shrinks ur testicles.
thank god those free cookies at the supermarket said yellow 5 free. now i dont have to worry about my testicles shrinking.
by moon August 01, 2004
 
4.
Not only shrinks tesiticles. its been scientifically proven to reduce penis size as well.
I drank mtn dew with Yellow 5 and now i'm 2in.
by digerra November 15, 2005