Pencil test (breasts)
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The pencil test is an informal test of breast development and the need to wear a bra. It was published in a 1971 advice column by Ann Landers mostly containing reader responses, pro and anti-bra, to her recent column "berating the braless female who shamelessly bounced and flopped and went shopping ... [which for Landers] created a deluge of mail". One Chicago correspondent chimed in:[1][2]
The question "to bra or not to bra" can be easily answered if the undecided woman will apply this test to herself. Take an ordinary woodcase pencil. Put it under one breast. If the pencil stays there you should wear a bra. If it falls, you can go braless.
— One Who Flunked
The implication is that breasts that are not pendulous enough to trap a pencil are self-supporting and do not need the added support of a bra.
Some girls see the ability of their breast holding a pencil (or even a box of cereal) as a sign that they are finally a grown-up woman.[3]
No evidence has been offered as to its validity, but some people consider it a method to determine whether a young girl should begin wearing a bra. The theory is that if the girl places a pencil under her breast and it stays in place, then wearing a bra is recommended; if it falls to the ground, a bra is not yet needed.[4][5] Other factors when choosing whether to wear a bra include physical support of very large breasts, pain when exercising, and general comfort.