Sexual penetration may be painful when there is not enough moisture in the vagina or when the tissue lining the vagina becomes fragile because of lower estrogen levels. The vaginal canal may actually shorten, and the opening may become more closed. Several methods are available to help. One of the most effective is frequent sexual activity. Other remedies include short-acting, water-based lubricants, such as Astroglide or K-Y lubricants, that supply moisture immediately before intercourse. Long-acting vaginal moisturizers are also available (such as Replens and Revaree), while prescription estrogen-based vaginal creams, rings or tablets may also help. Lubricants described as "warming" or "stimulating" may cause vaginal or vulvar irritation.