The penis is sometimes large and sometimes small may be the state when erect and not erect, belong to the normal physiological phenomenon. The penis is mainly composed of the corpus cavernosum, which consists of many cavernous trabeculae and cavities that are actually connected to blood vessels. When these cavities are filled with blood, the penis will become thicker and harder and erect. When the chambers are not engorged with blood, the penis becomes smaller and softer. Whether the chambers are engorged with blood or not is affected by a variety of factors such as body temperature, hormones, and libido, so as long as there is no discomfort, it is normal. If there is redness, swelling, pain, itching sensation in the penis, and you will feel pain during erection, it may be caused by local inflammation, and it is recommended to consult a doctor to clarify the cause.