oh and another thing,why are guys so attracted to breast?
The sexualization of breasts is far from universal. A study by anthropologists Clellan Ford and Frank Beach found that, of different societies they studied, as many had a noted preference for "plump body build" in women as had a preference for breasts (and among breasts, the preference ranged from "long and pendulous" to "upright, hemispherical breasts" to the especially popular "large" ones). Carolyn Latteier, in Breasts: the Women's Perspective on an American Obsession, says that when anthropologist Katherine Dettwyler "told women in Mali that Americans think breasts are sexually arousing, they were horrified." And amused: "'You mean men act like babies,' they shrieked, collapsing in laughter."
Even in European-based societies, breasts have not always been in fashion. Stomachs were more popular in the Middle Ages (no pun intended!); even in the 20th century, breasts have gone in and out of style. But one thing is constant: as long as they're considered attractive, the nipple is where the action is.
Why is this? What is this preoccupation with breasts revealed and concealed, and why is the nipple the sticking point, the one and only part of the breast that needs to be covered, the thing that, seen through cotton, can stimulate shaky adolescent boys into onanistic fervor?
Sigmund Freud had an idea about this. In the Freudian schema, the breast is a substitute for the penis. The initial stage of erotic development, after all, is the oral phase, where the baby sucks on the breast and receives passive comfort from it. After going through the control-focused anal stage (where anus and feces substitute for mouth and breast), the human finally comes to the phallic stage. As Latteier explains, "the vagina is supposed to stand in for the mouth and the penis for the breast." So nipples peeking through cotton are like a "boner" seen through the pants. They're sexually aggressive, and they're suggestive of erection and intercourse. The feeling imagined in seeing them transfers to the male's equivalent parts.
Not everyone thinks Freud was right. The famed (and in some quarters infamous) Masters and Johnson, in Human Sexual Response, detail findings that suggest an alternative. They point out what is already well-known in many quarters: prominent nipples are a sign of sexual arousal. When a woman is aroused, her nipples become erect and can elongate by up to a centimetre. The breast as a whole also swells. So a pointy nipple is like a little "I'm horny" flag. Desmond Morris, in his seminal book The Naked Ape, makes note of the same fact. (But Marilyn Yalon, in A History of the Breast, quotes a model who describes using ice to make her nipples pointy for photo shoots - hardly an aroused or pleasurable state!)
Interestingly, breasts that have nursed tend to swell less. This keys into an important fact about desire for breasts as a whole: in every society where breasts are sexualized, the ideal breast is one that does not show signs of age or nursing. As Nancy Etcoff notes in Survival of the Prettiest, the preferred form is always "firm and upward tilting," as on "young nulliparous females" ("nulliparous" means they've never borne children). The male preference is normally for the young, the fresh, the virginal, who will produce offspring of unquestionable parentage and who also arouse a protective instinct by virtue of their childlikeness. And the pointy nipples are an indicator of youth, less found in older women.
It is possible, of course, for more than one of these factors to be operative in the desire for nipples. The commonness of male oral contact with female nipples at the time of intercourse (almost 90% of couples do this) lends a certain weight to Freud's ideas. The penis-nipple equivalency actually works well with the nipple-as-sign-of-arousal. And it can't be denied that perky nipples are associated with nubile young women. So, while further studies are needed to provide any definitive answer (and I for one will volunteer to help with the observations), we do have the question fairly well in hand.
There is one matter left, however: the attractiveness of nipples viewed through fabric, as opposed to that of bare ones. This, too, is a matter of cultural variance, and puritanical attitudes have a determining effect. In the United States, as Marilyn Yalon says, "uncovered breasts are all the more precious because they are scarce." But covered ones, in the dialectic of temptation and reward, concealment and revealment, are more desirable to many.