Question:
Is there any halachic concern regarding the use of a tampon by a girl or woman?
Answer:
There is no halachic concern with the use of a tampon, whether for an unmarried girl or a married woman. The concern some have is that using a tampon could tear the hymen, and therefore a woman might no longer be halachically considered a besulah [i.e. Mukas Eitz] regarding marriage and her Kesuba. However, from a medical perspective the hymen is a flexible tissue that naturally stretches and can change for many reasons unrelated to tampon use, such as normal physical activity. In most cases, using a tampon does not cause any significant change, and even when minor stretching or small tearing occurs, it is not medically meaningful or unique to tampon use.
Sources:
See Asia 57 p. 72; Magen Avos E.H. p. 257