Most of the data on the long-term health effects of hormones come from studies in which hormones (estrogen alone or estrogen plus progestin) are administered orally in the form of pills. Hormones in the form of transdermal patches or gels are also used to treat menopause-related symptoms. Estrogen-containing vaginal creams and rings can be used specifically for vaginal dryness. Progesterone is also available as a pill or gel. The amount of estrogen that enters the bloodstream from estrogen-containing vaginal creams and rings depends on the types of hormones and the dose. Generally, vaginal administration of hormones results in lower levels of circulating hormones compared with an equivalent oral dose. Because the vaginal epithelium (thin layer of tissue that covers the vagina) responds to very small doses of estrogen, low-dose estrogen-containing creams or gels can be used.
This answer is based on source information from the National Cancer Institute.