點解褲襠的拉鍊位會經常隆起????

我成日著牛仔褲出街個時褲襠的拉鍊位會經常隆起....成日將佢按番平佢又隆番起....我覺得非常麻煩同肉酸~"~我明明一定無勃起...點解會咁...
究竟係咪條褲既腰圍問題??(我自己高腰28寸...條褲31寸著低腰),定係條褲既質地問題呢??
(因為我好多褲都係咁...係1~2條唔會)...搞到我明明好靚既levis都唔著得=.=
麻煩有無d著牛仔褲好叻既人答下我丫...呢個問題困擾左我好耐都唔知點解....而且解決唔到~"~