Candida is a yeast that already lives on and inside most people’s bodies, found naturally in the mouth, gut, and vaginal tract. You don’t “catch” it the way you catch a cold. Instead, candida infections happen when something disrupts the balance that normally keeps this yeast in check, allowing it to multiply and shift into an invasive form. The CDC confirms that candidiasis does not spread between people. Understanding what tips that balance is the key to understanding how candida infections develop.
Candida Already Lives in Your Body
Most people carry Candida albicans as a harmless resident of their digestive and genital tracts from early in life. In its normal state, candida exists as round, single-celled yeast that coexists peacefully with the bacteria and other microorganisms that make up your microbiome. These neighboring bacteria compete with candida for nutrients and space, and they produce compounds that actively suppress its growth.
The trouble starts when candida switches from that harmless yeast form into an elongated, thread-like form called hyphae. In this shape, it can burrow into tissue, attach to surfaces, and spread. This shape-shifting is triggered by environmental signals: low oxygen, changes in pH, and certain sugars all flip the switch. Your gut naturally contains many of these triggers, but a healthy bacterial community keeps candida in check despite them.
Antibiotics Are the Most Common Trigger
Broad-spectrum antibiotics are one of the most well-documented causes of candida overgrowth. When antibiotics kill off large populations of bacteria in your gut, they don’t just remove competitors for space. They fundamentally change the chemical environment. Research published in FEMS Microbiology Ecology found that antibiotic-treated mice had significantly higher levels of simple sugars and certain bile acids in their intestines, both of which actively promote candida’s shift into its invasive form. At the same time, antibiotic use reduced levels of secondary bile acids and short-chain fatty acids that normally inhibit candida growth.
In practical terms, this means a course of antibiotics can simultaneously remove the bacteria that keep candida suppressed and create a chemical environment that encourages it to become aggressive. This is why vaginal yeast infections so commonly follow a round of antibiotics for a completely unrelated problem like a sinus infection or urinary tract infection.
Blood Sugar and Diabetes
Elevated blood sugar creates a favorable environment for candida, and the threshold is lower than many people realize. A study comparing people with prediabetes to healthy controls found that 100% of the prediabetes group carried oral candida, compared to about 66% of the control group. Candida albicans specifically was found in nearly 49% of the prediabetes group versus 26% of controls. These were people with fasting blood glucose levels between 100 and 125 mg/dL and A1c levels between 5.7% and 6.4%, numbers that many people walk around with without knowing.
The mechanism is straightforward: candida feeds on sugar. Higher glucose in your blood means higher glucose in your saliva, vaginal secretions, and other body fluids. For people with uncontrolled type 2 diabetes, recurrent yeast infections are sometimes the symptom that leads to diagnosis. If you’re getting frequent candida infections and haven’t had your blood sugar checked recently, it’s worth looking into.
Hormonal Changes
Estrogen plays a direct role in vaginal yeast infections. High estrogen levels increase the amount of glycogen (a stored sugar) in vaginal tissue, which feeds candida. This explains why yeast infections are more common during pregnancy, while taking combination birth control pills, and during hormone replacement therapy that includes vaginal estrogen. An estimated 75% of women will have at least one vaginal yeast infection in their lifetime, and 40% to 45% will have two or more.
The flip side is also true. After menopause, when estrogen drops, some women experience fewer yeast infections. But if a doctor prescribes vaginal estrogen to help with dryness or other menopausal symptoms, yeast infections can return. This doesn’t mean estrogen-containing treatments should be avoided, just that the connection is worth knowing about so you can recognize symptoms early.
Weakened Immune System
Your immune system is the primary reason candida stays in its harmless form. Anything that suppresses immune function raises your risk. This includes HIV/AIDS, chemotherapy, organ transplant medications, and long-term corticosteroid use (including high-dose inhaled steroids for asthma, which can cause oral thrush if you don’t rinse your mouth after each dose).
Even temporary immune suppression from stress, poor sleep, or illness can be enough to allow a localized overgrowth, particularly in areas where candida is already present in higher numbers like the mouth or vaginal tract.
Moisture, Heat, and Skin Infections
Candida thrives in warm, moist environments. Skin infections tend to appear in areas where skin folds trap moisture: the armpits, groin, under the breasts, and between fingers or toes. Tight-fitting synthetic clothing that doesn’t breathe, wet swimsuits worn for extended periods, and sweaty workout clothes all create conditions candida loves. Diaper rash in infants is often a candida skin infection, since diapers create exactly the warm, moist, enclosed environment the yeast needs.
Keeping skin dry and exposed to air is one of the simplest ways to prevent these infections. Wearing breathable fabrics, changing out of wet clothing promptly, and drying skin folds thoroughly after bathing all reduce risk.
It’s Not Contagious, but Context Matters
The CDC states clearly that candidiasis does not spread between people. You can’t pick it up from a toilet seat, a swimming pool, or casual contact. Vaginal yeast infections are not classified as sexually transmitted infections. While sexual activity can occasionally irritate tissue enough to trigger symptoms in someone already carrying candida, the infection itself isn’t being transmitted from one partner to another.
The one exception worth noting is in healthcare settings, where invasive candida infections can develop when the yeast enters the bloodstream through central IV lines, surgical wounds, or other medical devices. This is a hospital-acquired infection related to breaks in the skin barrier, not person-to-person spread. Healthcare workers prevent this through hand hygiene and proper device care, not isolation precautions.
Why Some People Get Recurring Infections
If you get candida infections repeatedly, it usually means an ongoing underlying factor is keeping conditions favorable for overgrowth. The most common culprits are frequent antibiotic use, chronically elevated blood sugar (even at prediabetic levels), hormonal factors, or immune suppression. Sometimes multiple factors overlap: a person with mildly elevated blood sugar who takes antibiotics twice a year and wears tight clothing is stacking risk factors.
Identifying and addressing the root cause is more effective than treating each infection as a one-off event. For some people, that means better blood sugar management. For others, it means discussing antibiotic alternatives with a doctor or switching to breathable cotton underwear. The yeast itself isn’t the problem. It’s always there. The question is what’s allowing it to take over.