Seborrheic Keratosis. Freezing with liquid nitrogen (cryosurgery). Cryosurgery can be an effective way to remove seborrheic keratoses. However, it may not work on large, thick growths, and it may lighten the treated skin (hypopigmentation). Cryosurgery is more effective at the doctors office because it is much colder, -320 vrs -55 from otc products.