Small lumps inside the right breast may be caused by the following reasons. First of all, some people will have irregular, ill-defined lumps inside their breasts during the premenstrual period, which are also often accompanied by pain. As soon as menstruation passes, the lump will become smaller and disappear, its no problem and no harm to the body. Secondly, if the androgens in a woman’s body stimulate excessive proliferation of breast tissue, a breast fibroid will form. The lumps are usually smooth and do not feel painful and have no bad effects on the body. This disease will be more likely to occur in young patients in the population, especially between the ages of 20-25. Finally, it will be worse is breast cancer, but most of them occur in middle-aged women and less often in young people.