The parotoid gland is a large external skin gland found on the head and shoulders of many amphibians, most notably true toads (family Bufonidae). These paired glands form swellings behind the eyes and produce a complex mixture of chemicals that are expelled onto the skin surface when the animal is threatened. The glands are a normal anatomical feature, not a disease or infection.
Structure and location
Parotoid glands are macroglands composed of dense secretory tissue derived from the amphibian integument. Unlike small mucous glands, they are often visible as raised patches or ridges on the dorsum and posterior to the eyes. The location and size vary by species: in some toads they are obvious and roughly oval, in others they are smaller or less conspicuous. Although they may resemble skin warts, parotoid glands are not caused by viruses and are not contagious to humans or other animals.
Secretions and physiological effects
The material released from parotoid glands typically contains steroidal compounds (sometimes collectively called bufadienolides or bufagenins), biogenic amines and alkaloids, and other substances including bufotenine in some species. These secretions can be irritating to mucous membranes and, in sufficient quantities, toxic to predators or household pets. The toxins act as chemical deterrents rather than injected venoms: they discourage predation by taste, smell, or by causing physiological effects if absorbed or ingested. For more on amphibian toxins see toxin summaries and specific notes on the active compounds at bufotoxin information.
Function, ecology and behavior
Parotoid glands serve primarily as defensive structures. Many amphibians display aposematic colors or posture to advertise the presence of toxic secretions, and predators learn to avoid animals that produce unpleasant tastes or adverse effects. When handled or bitten, amphibians may squeeze or exude glandular fluids; some species also combine visual displays with the chemical defense for greater effectiveness. These glands thus play a role in survival, predator–prey interactions and, indirectly, in the evolution of warning signals among amphibians.
Human interactions, myths and notable facts
A common misconception is that handling toads causes human warts. Human warts are caused by human papillomaviruses and are not transmitted by contact with amphibian skin. Parotoid glands may look wart-like, which likely contributed to this myth. People should nevertheless avoid handling wild amphibians unnecessarily because glandular secretions can irritate skin or eyes, and because amphibians are sensitive to human-borne oils and contaminants. Parotoid secretions have also drawn attention in ethnobiology and pharmacology for their bioactive compounds, but any traditional or experimental use should be approached with caution due to toxicity. For general species accounts that mention parotoid glands see amphibian anatomy resources, frogs and toads overview, and conservation notes for salamanders at salamander pages.
- Common in: many toads and some frogs and salamanders.
- Main role: chemical defense via toxic skin secretions.
- Appearance: raised, wart-like swellings; normal anatomy, not disease.
- Safety: not a source of human warts, but secretions can irritate or be toxic if ingested.