Antibiotics kill off the 'good' bacteria which control the growth of yeasts. Some antibiotics are particularly associated with causing thrush. If your blood sugar levels are poorly controlled, yeasts may grow out of control. Some drugs, for example steroids and drugs which suppress the immune system, encourage the growth of yeasts or interfere with the body's control mechanisms. Many women get their first attack of thrush when they are pregnant.
Pregnancy seems to produce an ideal environment for yeasts to grow.
Older contraceptive pills containing high doses of oestrogen were found to make some women more susceptible to thrush, but the new lower dose contraceptives have smaller amounts of hormones and seem less likely to trigger thrush. You may notice that thrush often develops before a period, possibly due to hormonal changes. Some women find that using bath oils, perfumed soaps or vaginal deodorants seem to cause thrush. Sexual intercourse may also bring on an attack of thrush or make symptoms worse. This soothes the tissues and prevents growth of yeasts.