The causes of pre-menstrual mouth ulcers are varied, specifically for the following reasons: 1. It is because of bacterial infections, such as staphylococcus, staphylococcus aureus or oral candida. Because before menstruation, the metabolic level as well as the immunity and resistance of the female organism will be reduced. When the immunity decreases, it is easy to cause bacteria to take advantage of the situation, which leads to pre-menstrual ulcers. 2, because the female endocrine dysfunction, or irregular diet often eat spicy, irritating food and lead to. The emotional changes of women before menstruation may also fluctuate, such as increased stress, fatigue, etc. may also cause mouth ulcers. Other causes may be fire, for which you can drink herbal remedies to clear heat and detoxify.