When a vacuum is used on pleasurable areas, they increase the flow of blood to the body part. For a penis, increased blood flow can change the appearance, making it look larger and harder, and feel more sensitive. Most of the Enlargers listed are manually operated, which allow the user to personalize the level of girth to their preference. For vulvas and clitorises, pumps increase the amount of blood flowing into desired areas, making it feel more sensitive and excited. Using a pump helps to have more control over the amount of pressure. Some of the pumps also have a sucking feature, which creates a sensation that is similar to sucking or oral sex. Depending on the design, they can be used on penises, clitorises, vulvas, or nipples.