A toxin (from Ancient Greek: τοξικόν toxikon) is a poisonous substance produced within living cells or organisms; man-made substances created by artificial processes are thus excluded. The term was first used by organic chemist Ludwig Brieger (1849–1919).

For a toxic substance not produced within living organisms, "toxicant" and "toxics" are also sometimes used.^{[citation needed]}.

Toxins can be small molecules, peptides, or proteins that are capable of causing disease on contact with or absorption by body tissues interacting with biological macromolecules such as enzymes or cellular receptors. Toxins vary greatly in their severity, ranging from usually minor and acute (as in a bee sting) to almost immediately deadly (as in botulinum toxin).

Toxins are often distinguished from other chemical agents by their method of production - the word toxin does not specify method of delivery (compare with venom and the narrower meaning of poison – all substances that can also cause disturbances to organisms). It simply means it is a biologically produced poison. There was an ongoing terminological dispute between NATO and the Warsaw Pact over whether to call a toxin a biological or chemical agent, in which the NATO opted for biological agent, and the Warsaw Pact, like most other countries in the world, for chemical agent.^{[citation needed]}

William Robert "Will" Young (born 20 January 1979) is a British singer-songwriter and actor who came to prominence after winning the 2002 inaugural series of the British music contest Pop Idol, making him the first winner of the now-worldwide Idols-format franchise. His debut single, "Anything is Possible", was released two weeks after the show's finale and became the fastest-selling debut single in the United Kingdom.

As a teenager, Young studied politics at the University of Exeter before moving to London, where he pursued a musical theatre degree at the Arts Educational School. Although enrolled in a three-year programme, Young put his studies on hold in late 2001 to become a contestant on Pop Idol. After winning the competition the following year, he released his debut album From Now On (2002) which went to straight to number one. Friday's Child (2003) followed one year later and enjoyed greater popularity, eventually going platinum five times in the UK and spawning three top five singles. Achieving similar success, the album's successors include the multi-platinum Keep On (2005) and platinum Let It Go (2008) with his most recent release Echoes (2011) becoming his third UK number-one album.

Robert H. Lustig, MD is Professor of Clinical Pediatrics, at the University of California, San Francisco (UCSF). He is nationally recognized in the field of neuroendocrinology, with an emphasis on the regulation of energy balance by the central nervous system. He has a special interest in childhood obesity. He has become publicly notable through his efforts to draw attention to the effects that the natural sugar fructose can have on human and especially children's health if consumed in large amounts. On May 26, 2009, Lustig gave a lecture called “Sugar: The Bitter Truth” which was posted on YouTube the following July and has become a viral success with over nearly 2.5 million viewings (as of Jun 2, 2012). In this lecture, Lustig notably calls fructose a "poison" and compares its metabolic effects with those of ethanol. Lustig is particularly critical of the widespread use of high-fructose corn syrup in the United States.

Lustig grew up in Brooklyn, New York, and attended Stuyvesant High School in Manhattan. He obtained his bachelors degree from MIT in 1976, and received his M.D. from Cornell University Medical College in 1980. From there, he spent six years as a research associate in neuroendocrinology at The Rockefeller University. He performed his pediatric residency at St. Louis Children's Hospital, and his clinical fellowship at UCSF which he joined in 1984.