Why Thrush Happens Before a Period, and the Role of MCAS

Many women experience vaginal thrush in the week before their period. It often feels sudden and frustrating, especially when you are eating well and taking care of yourself. There is a clear physiological reason for this pattern, and for some women, MCAS adds another layer that makes symptoms worse.

The Hormonal Shift Before a Period

Just before your period, estrogen levels drop. Estrogen normally keeps the vaginal lining thick, well lubricated and naturally acidic. When estrogen falls, the vaginal environment becomes less acidic and more vulnerable. This creates conditions that allow Candida to grow easily.

At the same time, progesterone rises earlier in the luteal phase and then falls. Higher progesterone slows movement in the gut and vagina, reduces local immunity and increases moisture retention. This combination can encourage yeast overgrowth.

Changes in Immunity and Blood Sugar

The immune system naturally dips just before the period begins. This is part of the menstrual cycle. A slight reduction in immune surveillance means Candida can take advantage.

Blood sugar often rises in the late luteal phase as the body becomes temporarily more insulin resistant. Even small increases in glucose can feed vaginal yeast and make symptoms more noticeable.

How MCAS Contributes

Women with mast cell activation often experience stronger premenstrual symptoms in general. Hormonal shifts trigger mast cells to release histamine. Histamine causes inflammation and disrupts the vaginal microbiome. When the microbiome becomes imbalanced, yeast grows more easily.

MCAS also contributes to higher baseline inflammation, more gut permeability and greater microbiome disruption, all of which increase susceptibility to thrush before a period.

Other Factors That Make Thrush More Likely

• antibiotic use

• high sugar or refined carbohydrate intake

• tight clothing• stress

• poor sleep•

synthetic underwear

• low estrogen states

• sexual activity that changes vaginal pH

• HRT that does not adequately support the vaginal tissues

How to Reduce Premenstrual Thrush

1. Stabilise blood sugarLower sugar swings during the week before your period reduce yeast growth.

2. Support estrogen where appropriateVaginal estrogen can restore acidity and strengthen the lining.

3. Use targeted probioticsLactobacillus rhamnosus and Lactobacillus reuteri help restore a balanced vaginal microbiome.

4. Reduce histamine load if you have MCAS.

5. 2 pm antihistamine, bedtime antihistamine if needed and DAO before meals can help stabilise mast cells.

6. Avoid tight and synthetic clothingThis reduces moisture and friction.

7. Consider preventive measures in the late luteal phase

8. Short courses of clotrimazole pessaries can prevent predictable monthly flares.

When It Might Not Be Thrush

If symptoms recur every cycle or do not respond to typical treatment, consider possibilities such as low estrogen, bacterial vaginosis, lichen sclerosus, progesterone sensitivity, insulin resistance or thyroid dysfunction.

Dr Purity Carr