In cultures across pre-Christian Europe, mistletoe was seen as a representation of divine male essence (and thus romance, fertility and vitality), possibly because of a resemblance between the berries and semen.
According to Pliny the Elder, the Celts considered it a remedy for barrenness in animals and an antidote to poison.
When Christianity became widespread in Europe after the 3rd century AD, the religious or mystical respect for the mistletoe plant was integrated to an extent into the new religion. In some way that is not presently understood, this may have led to the widespread custom of kissing under the mistletoe plant during the Christmas season. The earliest documented case of kissing under the mistletoe dates from 16th century England, a custom that was apparently very popular at that time.
Mistletoe is commonly used as a Christmas decoration, though such use was rarely alluded to until the 18th century. Viscum album is used in Europe whereas Phoradendron serotinum is used in North America. According to custom, the mistletoe must not touch the ground between its cutting and its removal as the last of Christmas greens at Candlemas; it may remain hanging through the year, often to preserve the house from lightning or fire, until it is replaced the following Christmas Eve. The tradition has spread throughout the English-speaking world but is largely unknown in the rest of Europe.
The type of Mistletoe used during Christmas celebrations is of the same type as that believed to be sacred by ancient druids, but, outside northern Europe, the plant used is not the same species. The mistletoe that is commonly used as a Christmas decoration in North America (Phoradendron flavescens) grows as a parasite on trees in the west as also in those growing in a line down the east from New Jersey to Florida. In Europe, where the custom originates, the 'original' mistletoe, Viscum album, is still used. The European mistletoe is a green shrub with small, yellow flowers and white, sticky berries which are considered poisonous. Ancient druids considered the Viscum album plant holy, but had no knowledge of the Phoradendron flavescens. Modern druids focus on the parasitic habitat on oak (where it is very rarely found) as being the definer of a sacred mistletoe, and use Phoradendron flavescens as well as other mistletoe species.
According to ancient Christmas custom, a man and a woman who meet under a hanging of mistletoe were obliged to kiss. The custom may be of Scandinavian origin.
"The mistletoe is still hung up in farm-houses and kitchens at Christmas, and the young men have the privilege of kissing the girls under it, plucking each time a berry from the bush. When the berries are all plucked the privilege ceases.
Mistletoe leaves and young twigs are used by herbalists, and it is popular in Europe, especially in Germany, for treating circulatory and respiratory system problems. Use of mistletoe extract in the treatment of cancer originated with Rudolf Steiner, the founder of Anthroposophy. He compared the parasitic nature of the mistletoe plant to that of cancer, and believed that cancer represents a faltering of the body's spiritual defenses. Some anthroposophical mistletoe preparations are diluted homeopathically. Mistletoe extract is sold as Iscador, Helixor, and several other trade names.
Public interest in the United States was spurred in 2001 following actress Suzanne Somers' decision to use Iscador in lieu of chemotherapy following her treatment for breast cancer using surgery and radiotherapy.