The vaginal epithelium is the inner lining of the vagina consisting of multiple layers of (squamous) cells.

In the course of the reproductive cycle, the vaginal epithelium is subject to normal, cyclic changes, that are influenced by estrogen: with increasing circulating levels of the hormone, there is proliferation of epithelial cells along with an increase in the number of cell layers.

[9][12] Although hormone induced changes occur in the other tissues and organs of the female reproductive system, the vaginal epithelium is more sensitive and its structure is an indicator of estrogen levels.

[20] The cells of the vaginal epithelium retain a usually high level of glycogen compared to other epithelial tissue in the body.

[22] Vaginal epithelium forms transverse ridges or rugae that are most prominent in the lower third of the vagina.

[23][24][9] This layer of epithelium is protective, and its uppermost surface of cornified (dead) cells are unique in that they are permeable to microorganisms that are part of the vaginal flora.

[7] The junctions between epithelial cells regulate the passage of molecules, bacteria and viruses by functioning as a physical barrier.

[8] The cervical mucus that is located inside the vagina can be used to assess fertility in ovulating women.

[27] During the luteal and follicular phases of the estrous cycle the structure of the vaginal epithelium varies.

The glycogen from these cells is converted to sugars and then fermented by the bacteria of the vaginal flora to lactic acid.

The metabolism of this complex sugar by the lactobacillus dominated microbiome is responsible for vaginal acidity.

[34][35][36] The cellular junctions of the vaginal epithelium help prevent pathogenic microorganisms from entering the body though some are still able to penetrate this barrier.

The permeability of epithelium thus provides access for these immune system components to prevent the passage of invading pathogens into deeper vaginal tissue.

[9] The epithelium further provides a barrier to microbes by the synthesis of antimicrobial peptides (beta-defensins and cathelicidins) and immunoglobulins.

These protective mechanisms are due to frequent exfoliation of the superficial cells, low pH, and innate and acquired immunity in the tissue.

Research into the protective nature of the vaginal epithelium has been recommended as it would help in the design of topical medication and microbicides.

[32] The use of nanoparticles that can penetrate the cervical mucus (present in the vagina) and vaginal epithelium has been investigated to determine if medication can be administered in this manner to provide protection from infection of the Herpes simplex virus.

[49] Nanoparticle drug administration into and through the vaginal epithelium to treat HIV infection is also being investigated.