Origins
Melatonin was named for pigment, not for sleep. Aaron Lerner, a dermatologist at Yale University, coined the term in 1958 after isolating a hormone from bovine pineal glands that could lighten frog skin by contracting the melanin-containing cells called melanophores. He combined mela- from melanin (the dark pigment, from Greek melas meaning black) with -tonin from Greek tonos (tone or tension), describing a substance that tones or modulates dark pigment.
The discovery had nothing to do with sleep. Lerner was researching skin pigmentation disorders, particularly vitiligo. He spent four years processing over 200,000 bovine pineal glands to extract enough melatonin for analysis. The connection between melatonin and circadian rhythms emerged gradually through the 1960s and 1970s, as researchers realized the pineal gland produced melatonin in response to darkness and suppressed it during daylight.
The Greek root melas (black, dark) appears across English in melanin, melanoma (a dark-pigmented skin cancer), and melancholy (originally black bile, one of the four humors thought to cause depression). The -tonin suffix links melatonin to serotonin, its chemical precursor. The pineal gland converts serotonin into melatonin as daylight fades, creating a direct biochemical bridge between the two molecules.
Later History
Melatonin entered popular awareness in the 1990s when it became available as an over-the-counter supplement in the United States. It is now one of the most widely used sleep aids globally, though its regulatory status varies by country — it requires a prescription in most of Europe but is sold freely in American pharmacies.
The word's etymology is a reminder that scientific names often preserve the circumstances of discovery rather than the function most associated with a substance. Melatonin will forever carry the mark of frog skin experiments in its name, even though most people associate it with falling asleep.