Vulvovaginal Candidiasis (yeast infection)

Overview

Vulvovaginal candidiasis (VVC) is a highly prevalent fungal infection predominantly caused by Candida albicans and occasionally by non-albicans species such as C. glabrata and C. krusei. It affects approximately 70-75% of women at least once in their lifetime, with 5-8% experiencing recurrent vulvovaginal candidosis (RVVC), defined as four or more symptomatic episodes per year.^[1] The disease manifests as an acute inflammatory condition of the vulva and vaginal mucosa, characterized by itching, burning, redness, and abnormal vaginal discharge. The pathogenesis is multifactorial, involving complex interactions among the Candida species’ virulence factors, host immune responses, estrogenic environment, and vaginal microbiome, primarily Lactobacilli.^[2] Candida’s ability to switch between yeast and hyphal forms, form biofilms, and secrete toxins such as candidalysin contributes to infection persistence and symptom severity. Diagnosis remains challenging due to the presence of Candida as a commensal in many asymptomatic women.^[3] Treatment mainly relies on azole antifungals, though increasing azole resistance, especially among non-albicans species, complicates management.^[4][5] Long-term maintenance antifungal regimens are often necessary for RVVC but are associated with risks of resistance and relapse. Patient quality of life is significantly affected due to physical discomfort, psychological burden, and impaired sexual health. Advancing diagnostic accuracy, understanding microbiome-host interactions, and developing novel therapeutics are critical needs for improving clinical outcomes.

Associated Conditions

RVVC is linked with several associated conditions that modulate susceptibility and severity. High estrogen states such as pregnancy, use of oral contraceptives, and hormone replacement therapy increase the risk by altering vaginal immunity and microbiome balance.^[6] Diabetes mellitus and immunosuppressive states, including HIV infection, also predispose women to frequent recurrences.^[7][8] Antibiotic usage disrupts the protective Lactobacillus-dominant vaginal microbiota, facilitating Candida overgrowth.^[9] Behavioral factors such as frequent sexual intercourse, use of poorly ventilated clothing, and atopic diseases may contribute to susceptibility. Genetic polymorphisms affecting innate immune signaling pathways have been implicated in impaired fungal clearance and enhanced inflammation. These factors, individually or in combination, create a permissive environment for Candida pathogenicity and chronic infection.

Causal Theories

The etiology of VVC remains incompletely understood and is recognized as multifactorial. The primary causal theory revolves around an imbalance between Candida virulence mechanisms and host immune defenses. Candida albicans employs a polymorphic lifestyle, switching from benign yeast to invasive hyphal forms, secreting enzymes and candidalysin that promote tissue invasion and inflammation. Biofilm formation further shields Candida from antifungal agents.^[10] Host factors impair fungal clearance, including estrogen-driven changes, neutrophil dysfunction, and genetic variants in pattern recognition receptors. The vaginal microbiome, particularly Lactobacilli, usually suppresses Candida growth; disruptions to this ecosystem via antibiotics or other factors remove this inhibition.^[11] Limitations in current causal theories include insufficient understanding of the triggers converting asymptomatic colonization into symptomatic infection and the role of non-cultivable fungal species. Novel hypotheses suggest that immunological hypersensitivity to Candida antigens may drive symptoms independent of fungal load, highlighting the complexity of RVVC pathogenesis.^[12]

Theory	Description
Candida Virulence & Morphogenesis	Candida’s morphological switching and virulence factor secretion lead to tissue damage
Host Immune Dysfunction	Genetic and functional immune defects impair fungal clearance
Microbiome Dysbiosis	Disruption of Lactobacillus-dominated vaginal flora facilitates Candida overgrowth
Hypersensitivity Response	Exaggerated inflammatory reaction to Candida antigens causes symptoms

Diagnosis

Accurate diagnosis of VVC requires confirmation of Candida presence combined with clinical symptoms. Conventional diagnosis relies on clinical examination, microscopy to detect pseudohyphae or blastospores, and culture to identify Candida species.^[13] However, microscopy sensitivity ranges from 50-80%, and culture may be slow or inconclusive. Molecular methods such as PCR enhance detection sensitivity and can identify mixed or resistant strains, but are not widely accessible.^[14] Identification of Candida species is crucial, as non-albicans species often exhibit reduced susceptibility to azoles. Antifungal susceptibility testing is recommended in refractory cases.^[15] Emerging research into microbiome and metabolomic signatures holds promise for non-invasive diagnostics that distinguish colonization from infection and identify treatment-resistant profiles.^[16] Nonetheless, lack of point-of-care rapid testing and inconsistent guideline adherence contribute to delayed or inappropriate treatment, underscoring the need for improved diagnostics integrating microbiome insights.

Primer

VVC cannot be fully understood without considering its relationship with the vaginal microbiome, where beneficial bacteria such as Lactobacillus species maintain an acidic environment that suppresses fungal overgrowth. Beyond microbial interactions, the vaginal environment’s metal content plays a vital role. Essential metals like zinc and copper are tightly controlled by the host through nutritional immunity mechanisms to restrict fungal growth. Meanwhile, Candida has evolved strategies to acquire these metals despite host defenses. This dynamic interplay between the host’s immune system, resident microbes, and metal availability forms a complex network that shapes the course of VVC and offers new directions for diagnosis and treatment.

Metallomic Signatures

The metallomic signature of VVC reflects how Candida albicans interacts with and adapts to metal stress in the host environment. Research shows that C. albicans can tolerate and even sequester high concentrations of toxic metals like chromium, lead, and zinc, using biosorption mechanisms involving its cell wall.[17]^[x] These adaptations not only enhance its survival in hostile environments but may also reinforce its biofilm structure and resistance to antifungal agents. Additionally, differential sensitivity to metals like cadmium and mercury indicates the presence of complex detoxification and efflux pathways, which may overlap with drug resistance mechanisms. From a therapeutic perspective, disrupting Candida’s metal homeostasis, or exploiting its biosorptive capacity, could offer novel treatment strategies, particularly in drug-resistant or recurrent VVC cases. This metallomic insight expands our understanding of the infection beyond microbiome shifts, adding a crucial chemical-ecological layer to host-pathogen interactions.

What is the Metallomic Signature of Vulvovaginal candidiasis?

Zinc (Zn

Zinc is a vital micronutrient that Candida albicans requires for enzymatic functions and virulence. The host restricts zinc availability through sequestration proteins like calprotectin, which bind zinc to limit fungal growth. In response, C. albicans expresses zinc scavenging proteins such as PRA1 and the high-affinity transporter ZRT1 to overcome this metal limitation.

Copper (Cu)

Copper serves dual roles as an essential cofactor and a potential toxin. The host limits copper access to Candida by sequestration, forcing the fungus to adapt by downregulating copper-dependent enzymes like SOD1 and upregulating manganese-dependent alternatives such as SOD3. Copper also exhibits antimicrobial properties that disrupt fungal respiration and ATP production.

Lead (Pb)

Lead is a toxic heavy metal to which Candida albicans shows biosorption ability. Although not essential for fungal growth, lead exposure influences fungal physiology and may affect biofilm formation. The full role of lead in VVC pathogenesis requires further study.

Cadmium (Cd)

Cadmium is highly toxic to Candida at low concentrations, showing 100% sensitivity even at 1 mM in clinical isolates. This suggests potential therapeutic applications, though cadmium toxicity limits clinical use.

Mercury (Hg) and Silver (Ag)

Both mercury and silver possess potent antifungal effects by inhibiting cellular respiration and enzymatic activity in Candida. Silver ions, in particular, demonstrate significant antifungal potential and are explored as topical treatments for resistant infections. Candida’s resistance to these metals is limited, highlighting their promise as adjunctive therapies.

Nutritional Immunity

Nutritional immunity is a key host defense mechanism in VVC, where the body restricts access to essential metals like zinc and copper to limit the growth and virulence of Candida albicans. During infection, immune cells such as neutrophils release calprotectin, a protein that tightly binds these metals, effectively starving the fungus of nutrients it needs to survive.^[18] In response, C. albicans activates specialized metal-scavenging systems, including the zinc-binding protein PRA1 and transporter ZRT1, and shifts its antioxidant defenses to rely on manganese when copper is unavailable.^[19] This ongoing struggle between host and pathogen, essentially a biochemical tug-of-war over micronutrients, plays a critical role in infection severity and persistence. When the vaginal microbiota, particularly protective Lactobacillus species, is disrupted, this defense can weaken, giving Candida a competitive edge.^[20] Understanding nutritional immunity not only sheds light on the pathogenesis of VVC but also suggests new therapeutic directions, including strategies that enhance host metal-binding defenses or target fungal nutrient acquisition systems.

References

1. Vulvovaginal Candidosis: Current Concepts, Challenges and Perspectives. Sustr, V., Foessleitner, P., Kiss, H., & Farr, A. (2020). (Journal of Fungi, 6(4), 267)
2. Microbiota in vaginal health and pathogenesis of recurrent vulvovaginal infections: a critical review. Kalia, N., Singh, J. & Kaur, M.. (Ann Clin Microbiol Antimicrob 19, 5 (2020))
3. Management of recurrent vulvovaginal candidosis: Narrative review of the literature and European expert panel opinion. Donders, G., Sziller, I. O., Paavonen, J., Hay, P., De Seta, F., Bohbot, J. M., Kotarski, J., Vives, J. A., Szabo, B., Cepuliené, R., & Mendling, W. (2022). (Frontiers in Cellular and Infection Microbiology, 12, 934353)
4. Vulvovaginal Candidosis: Current Concepts, Challenges and Perspectives. Sustr, V., Foessleitner, P., Kiss, H., & Farr, A. (2020). (Journal of Fungi, 6(4), 267)
5. Management of recurrent vulvovaginal candidosis: Narrative review of the literature and European expert panel opinion. Donders, G., Sziller, I. O., Paavonen, J., Hay, P., De Seta, F., Bohbot, J. M., Kotarski, J., Vives, J. A., Szabo, B., Cepuliené, R., & Mendling, W. (2022). (Frontiers in Cellular and Infection Microbiology, 12, 934353)
6. Estrogen promotes innate immune evasion of Candida albicans through inactivation of the alternative complement system. Kumwenda P, Cottier F, Hendry AC, Kneafsey D, Keevan B, Gallagher H, Tsai HJ, Hall RA.. (Cell Rep. 2022 Jan 4;38(1):110183)
7. Recurrent Vulvovaginal Candidiasis: An Immunological Perspective. Rosati D, Bruno M, Jaeger M, Ten Oever J, Netea MG.. (Microorganisms. 2020 Jan 21;8(2):144)
8. Candida species isolated from the vaginal mucosa of HIV-infected women in Salvador, Bahia, Brazil. Oliveira PM, Mascarenhas RE, Lacroix C, Ferrer SR, Oliveira RP, Cravo EA, Alves AP, Grassi MF.. (Braz J Infect Dis. 2011 May-Jun;15(3):239-44)
9. Interactions between Candida albicans and the resident microbiota. Li H, Miao MX, Jia CL, Cao YB, Yan TH, Jiang YY, Yang F.. (Front Microbiol. 2022 Sep 20;13:930495. doi:)
10. Management of recurrent vulvovaginal candidosis: Narrative review of the literature and European expert panel opinion. Donders, G., Sziller, I. O., Paavonen, J., Hay, P., De Seta, F., Bohbot, J. M., Kotarski, J., Vives, J. A., Szabo, B., Cepuliené, R., & Mendling, W. (2022). (Frontiers in Cellular and Infection Microbiology, 12, 934353)
11. Dual Mechanisms of Action: Anti-Candida and Anti-Inflammatory Potential of Lactobacillus Fermentation Broth in Treating Vulvovaginal Candidiasis. Horng H-C, Xu J-W, Kuo Y-S, Chen Y-S, Chiu Y-H, Tsui K-H, Tung Y-T.. (Journal of Fungi. 2025; 11(1):18)
12. Recurrent Vulvovaginal Candidiasis: An Immunological Perspective. Rosati D, Bruno M, Jaeger M, ten Oever J, Netea MG.. (Microorganisms. 2020; 8(2):144.)
13. Management of recurrent vulvovaginal candidosis: Narrative review of the literature and European expert panel opinion. Donders, G., Sziller, I. O., Paavonen, J., Hay, P., De Seta, F., Bohbot, J. M., Kotarski, J., Vives, J. A., Szabo, B., Cepuliené, R., & Mendling, W. (2022). (Frontiers in Cellular and Infection Microbiology, 12, 934353)
14. Clinical Evaluation of Polymerase Chain Reaction Coupled with Quantum Dot Fluorescence Analysis for Diagnosis of Candida Infection in Vulvovaginal Candidiasis Practice. Fan W, Li J, Chen L, Wu W, Li X, Zhong W, Pan H.. (Infect Drug Resist. 2023 Jul 25;16:4857-4865)
15. Identification of Candida species and susceptibility testing with Sensititre YeastOne microdilution panel to 9 antifungal agents. Kucukates E, Gultekin NN, Alisan Z, Hondur N, Ozturk R.. (Saudi Med J. 2016 Jul;37(7):750-7)
16. Mycobiome Study Reveals Different Pathogens of Vulvovaginal Candidiasis Shape Characteristic Vaginal Bacteriome. Zhao C,,Li Y, Chen B,Yue K,Su Z,Xu J, Xue W, Zhao G, Zhang L,,,2023.. (Microbiol Spectr11:e03152-22)
17. Biosorption of Heavy Metals by Candida albicans.. Rodríguez, I. A., Cárdenas-González, J. F., Juárez, V. M. M., Pérez, A. R., Zarate, M. de G. M., & Castillo, N. C. P. (2018). (InTech.)
18. Role of Calprotectin in Withholding Zinc and Copper from Candida albicans. Besold AN, Gilston BA, Radin JN, Ramsoomair C, Culbertson EM, Li CX, Cormack BP, Chazin WJ, Kehl-Fie TE, Culotta VC.. (Infect Immun. 2018 Jan 22;86(2):e00779-17)
19. Role of Calprotectin in Withholding Zinc and Copper from Candida albicans. Besold AN, Gilston BA, Radin JN, Ramsoomair C, Culbertson EM, Li CX, Cormack BP, Chazin WJ, Kehl-Fie TE, Culotta VC.. (Infect Immun. 2018 Jan 22;86(2):e00779-17)
20. The role of Lactobacillus species in the control of Candida via biotrophic interactions. Zangl I, Pap IJ, Aspöck C, Schüller C.. (Microb Cell. 2019 Nov 25;7(1):1-14)