Editing Melanin (section)

=== Pheomelanin ===
[[File:Pheomelanine.svg|thumb|Part of the structural formula of pheomelanin. "(COOH)" can be COOH or H, or (more rarely) other [[substituent]]s. The arrows denote where the polymer continues.]]
Pheomelanins (or phaeomelanins, from Greek φαιός ''phaios'', "grey") impart a range of yellowish to reddish colors.<ref>{{Cite journal |vauthors=Slominski A, Tobin DJ, Shibahara S, Wortsman J |date=October 2004 |title=Melanin pigmentation in mammalian skin and its hormonal regulation |journal=Physiological Reviews |volume=84 |issue=4 |pages=1155–228 |doi=10.1152/physrev.00044.2003 |pmid=15383650 |s2cid=21168932}}</ref> Pheomelanins are particularly concentrated in the lips, nipples, glans of the penis, and vagina.<ref>{{Cite web |year=2010 |title=pheomelanin |url=https://metacyc.org/META/NEW-IMAGE?type=COMPOUND&object=CPD-12380 |website=MetaCyc Metabolic Pathway Database |access-date=24 August 2019 |archive-date=11 February 2020 |archive-url=https://web.archive.org/web/20200211114047/https://metacyc.org/META/NEW-IMAGE?type=COMPOUND&object=CPD-12380 |url-status=live }} {{full citation needed|date=August 2014}}</ref> When a small amount of eumelanin in hair (which would otherwise cause blond hair) is mixed with pheomelanin, the result is orange hair, which is typically called [[red hair|"red" or "ginger" hair]]. Pheomelanin is also present in the skin, and redheads consequently often have a more pinkish hue to their skin as well. Exposure of the skin to ultraviolet light increases pheomelanin content, as it does for eumelanin; but rather than absorbing light, pheomelanin within the hair and skin reflect yellow to red light, which may increase damage from UV radiation exposure.<ref>{{Cite journal |last1=Thody |first1=A. J. |last2=Higgins |first2=E. M. |last3=Wakamatsu |first3=K. |last4=Ito |first4=S. |last5=Burchill |first5=S. A. |last6=Marks |first6=J. M. |date=August 1991 |title=Pheomelanin as well as eumelanin is present in human epidermis |url=https://pubmed.ncbi.nlm.nih.gov/2071942/ |journal=The Journal of Investigative Dermatology |volume=97 |issue=2 |pages=340–344 |doi=10.1111/1523-1747.ep12480680 |pmid=2071942 |access-date=25 September 2022 |archive-date=25 September 2022 |archive-url=https://web.archive.org/web/20220925140609/https://pubmed.ncbi.nlm.nih.gov/2071942/ |url-status=live }}</ref>

Pheomelanin production is highly dependent on [[cysteine]] availability, which is transported into the melanosome, reacting with dopaquinone to form cys-dopa. Cys-dopa then undergoes several transformations before forming pheomelanin.<ref name="Alaluf Heath Carter Atkins 2001 pp. 337–3472"/> In chemical terms, pheomelanins differ from eumelanins in that the oligomer structure incorporates [[benzothiazine]] and [[benzothiazole]] units that are produced,<ref>{{Cite journal |vauthors=Greco G, Panzella L, Verotta L, d'Ischia M, Napolitano A |date=April 2011 |title=Uncovering the structure of human red hair pheomelanin: benzothiazolylthiazinodihydroisoquinolines as key building blocks |journal=Journal of Natural Products |volume=74 |issue=4 |pages=675–82 |doi=10.1021/np100740n |pmid=21341762}}</ref> instead of DHI and [[DHICA]], when the amino acid [[L-cysteine]] is present.

Pheomelanins, unlike eumelanins, are rare in lower organisms<ref name=":0" /> with claims they are an "evolutionary innovation in the tetrapod lineage"<ref name="eumelanin" /> but recent research finds them also in some fish.<ref name="Xuetal" />