Toxic shock syndrome (TSS) is a potentially fatal bacterial illness. Scientists have recognized an association between TSS and tampon use, although the exact connection remains unclear.[21] TSS caused by menstrual cup use appears to be very rare to virtually nonexistent.[7][22] The probable reason for this is that menstrual cups are not absorbent, do not irritate the vaginal mucosal tissue, and so do not change the vaginal flora in any measurable amount.[23] Conversely, vaginal dryness and abrasions may occur if the tampon used is more absorbent than needed for the menstrual flow, and normal liquid that should line the vaginal wall is also absorbed.[21] Research has shown that the cup has no impact on the vaginal flora, which means there is no effect on the presence of S. aureus, the bacterium that can cause TSS.[23] The risk of TSS associated with cervical caps used for contraception in the female barrier method is also very low.[24] Cervical caps and menstrual cups both use mostly medical grade silicone or latex.