Vaginal discharge is mostly water, making up roughly 90 to 96% of its total weight. The rest is a complex mixture of shed skin cells, bacteria, mucus proteins, salts, immune molecules, and organic acids that together keep the vagina clean, lubricated, and protected from infection. What looks like a simple fluid is actually a dynamic blend of components that shifts throughout the menstrual cycle and across different life stages.
Water, Salts, and Acids
The liquid base of vaginal discharge is a filtrate that seeps through the vaginal walls from surrounding blood vessels. It carries dissolved electrolytes at concentrations that differ noticeably from blood. Sodium levels sit around 70 to 80 millimoles per kilogram, well below what you’d find in blood plasma. Potassium ranges between 20 and 40 millimoles per kilogram, with occasional spikes. These lower sodium levels help create an environment that favors beneficial bacteria over harmful ones.
The most important chemical feature of healthy discharge is its acidity. A normal vaginal pH falls between 3.8 and 4.5, which is roughly as acidic as a tomato. That acidity comes primarily from lactic acid, produced when resident bacteria break down glycogen (a sugar stored in vaginal lining cells). Before puberty and after menopause, pH tends to rise above 4.5 because lower estrogen levels mean less glycogen and fewer acid-producing bacteria.
The Bacteria Living in It
Healthy vaginal discharge contains millions of bacteria, and that’s a good thing. The dominant residents in most people are Lactobacillus species, the same family of bacteria used to make yogurt. These microbes convert glycogen into lactic acid, maintaining the acidic environment that suppresses harmful organisms. Two species matter most: one is considered the gold standard for vaginal health and provides strong protective functions, while another is the most common and abundant vaginal bacterial species worldwide but offers less consistent protection.
When Lactobacillus populations decline, other bacteria can overgrow. One hallmark of bacterial vaginosis is the appearance of “clue cells” under a microscope: these are normal vaginal skin cells that have become so coated with bacteria they look studded or stippled. The shift from Lactobacillus-dominant to mixed bacterial communities changes the discharge’s color, smell, and consistency, which is why changes in discharge often signal a shift in the microbial balance rather than an infection from outside.
Mucus Proteins and Their Structure
A significant portion of discharge comes from the cervix, which produces mucus made of enormous gel-forming proteins called mucins. These proteins are among the largest molecules the body makes, with single strands stretching up to 10 micrometers long. They interweave into a mesh-like gel that acts as a physical barrier, trapping bacteria and preventing them from traveling deeper into the reproductive tract.
The trapping mechanism is surprisingly specific. Sugar molecules on the surface of mucins bind directly to bacteria, physically catching them in the gel. White blood cells also get embedded in this mesh, where they can attack any pathogens that have been snared. This means the “stickiness” of cervical mucus isn’t just a texture. It’s an active defense system.
Immune Molecules and Antimicrobial Compounds
Vaginal discharge carries a surprisingly broad arsenal of immune molecules. The vaginal lining and cervix produce multiple types of antimicrobial peptides: small proteins that punch holes in bacterial membranes or interfere with their ability to reproduce. These include defensins, which target bacteria and fungi directly, and a compound called lysozyme that breaks down bacterial cell walls. Another protein, lactoferrin, starves bacteria by binding to iron they need to grow.
Other protective molecules include a protease inhibitor that shields vaginal tissue from damage during inflammation, and calprotectin, which is released by immune cells and has broad antimicrobial activity. Together, these compounds form a chemical defense layer that works alongside the acidic pH and beneficial bacteria. Even when you’re unaware of it, your discharge is actively fighting off potential infections around the clock.
Shed Cells and Enzymes
The vaginal walls are lined with layers of flat epithelial cells that constantly shed and replace themselves, much like skin. These discarded cells make up the whitish, slightly opaque quality of normal discharge. The shedding process, called desquamation, is a normal part of tissue maintenance and also helps physically flush bacteria and debris out of the vaginal canal.
Discharge also contains enzymes that play a balancing act. Some break down the sugar coatings on mucus proteins, which can be useful for recycling nutrients but can also become destructive during infections. When harmful bacteria like Gardnerella overgrow, they produce enzymes that aggressively degrade the protective mucus barrier, contributing to the thin, fishy-smelling discharge associated with bacterial vaginosis. In a healthy state, these enzymatic processes stay in check.
How Discharge Changes Through Your Cycle
If you track your discharge across a typical 28-day cycle, the shifts in volume, texture, and appearance directly reflect what’s happening with your hormones.
- Days 1 to 4 (after your period): Dry or tacky, usually white or slightly yellow. Very little volume.
- Days 4 to 6: Sticky and slightly damp, white in color.
- Days 7 to 9: Creamy, like a yogurt-like consistency. Wet and cloudy.
- Days 10 to 14 (around ovulation): Stretchy, slippery, and clear, resembling raw egg whites. This is the wettest point in your cycle and lasts about three to four days. The slippery texture exists to help sperm travel through the cervix.
- Days 15 to 28 (after ovulation): Thick and dry again, tapering off until menstruation starts. Rising progesterone and falling estrogen cause the cervical mucus to thicken and reduce in volume.
These changes are driven almost entirely by the ratio of estrogen to progesterone. Estrogen thins and increases cervical mucus, while progesterone thickens it. The total amount of fluid produced averages about a third of a gram per hour, though this varies widely from person to person and day to day.
What Color and Smell Tell You
Normal discharge ranges from clear to white or slightly off-white, and it either has no smell or a faintly sour scent from the lactic acid. The color and odor shift when the composition changes. A grayish, thin discharge with a fishy smell points to bacterial overgrowth, where acid-producing bacteria have been replaced by organisms that produce different chemical byproducts. A thick, white, cottage-cheese-like discharge typically signals a yeast overgrowth, where fungal cells and inflammatory debris replace the normal bacterial content. Yellow or green discharge, especially with a frothy texture, can indicate a different type of infection involving parasites or other organisms.
What’s worth knowing is that these visible and olfactory changes reflect real shifts in the underlying chemistry: the pH rising above 4.5, the Lactobacillus population dropping, antimicrobial peptides ramping up in response to invaders, and enzymes breaking down the protective mucus layer. The discharge you see is a readable signal of what’s happening at the molecular level.