The Toothache Plant (Acmella oleracea or sometimes Spilanthes acmella) is a unique flowering herb named for the powerful numbing sensation its flowers and leaves produce when chewed. The plant is easily recognized by its distinctive, small, round flower heads. These blooms are often olive-sized, featuring a vibrant gold or yellow base with a contrasting reddish-brown center. These unusual flowers have earned the herb nicknames such as “Eyeball Plant,” “Buzz Buttons,” and “Electric Daisy.”
Life Cycle and Regional Classification
The Toothache Plant’s status as a perennial depends entirely on the climate where it is grown. It is technically classified as a tender perennial, meaning it has the capacity to live for more than two years. Its native habitat is the warm, humid environments of South America, such as Brazil, where it thrives as a true perennial.
This herb is highly susceptible to frost, and freezing temperatures will cause it to die back completely. For this reason, in most temperate climates (USDA Hardiness Zones 9 and below), it is cultivated as an annual. Gardeners treat the plant as a seasonal crop, replanting it each spring after the last danger of frost has passed. Only in consistently warm, subtropical, or tropical locations (Zones 10–12) does it maintain its perennial status.
Essential Cultivation Requirements
To grow the Toothache Plant as an annual in cooler regions, gardeners should start seeds indoors six to eight weeks before the last expected frost date. This head start ensures the plant reaches maturity and produces an abundance of flowers. The tiny seeds require light for germination, so they should be surface-sown and gently pressed into the soil rather than covered deeply.
Once transplanted outdoors, seedlings require a location that receives full sun or very bright, direct light. As a tropical native, the plant prefers rich, well-draining soil that is high in organic matter. Incorporating compost into the planting area helps create the ideal medium for robust growth.
The Toothache Plant is water-hungry and shows distress quickly if the soil becomes too dry. It is important to keep the soil consistently moist throughout the growing season, but avoid waterlogging, which can lead to root rot. Fertilizing with a balanced, slow-release organic fertilizer at planting time supports vigorous growth until the first frost of autumn.
The Science Behind the Numbing Sensation
The numbing effect that gives the Toothache Plant its name is caused by Spilanthol, an N-alkylamide compound. This molecule is concentrated primarily in the flower heads, but is also present in the leaves and stems. When these parts are chewed, Spilanthol is released and interacts directly with sensory receptors in the mouth.
Spilanthol acts on the trigeminal nerve endings in the oral mucosa, producing distinct sensory experiences. The first sensation is often described as a strong tingling or buzzing feeling, quickly followed by a marked increase in salivation. This activity then progresses into a powerful local anesthetic effect that numbs the area.
Due to this anesthetic property, the plant has a long history of use in traditional herbal medicine for temporary relief from toothaches and mouth sores. The tingling quality of the herb has also made it an emerging culinary ingredient. Extracts containing Spilanthol are used as a flavoring agent in foods and beverages to provide a unique, electric sensation.