Latex is not to be confused withplant sap; it is a distinct substance, separately produced, and with different functions. The wordlatex is also used to refer to natural latexrubber, particularly non-vulcanized rubber. Such is the case in products like latexgloves, latexcondoms,latex clothing, andballoons.
TheIUPAC definition oflatex is "colloidal dispersion of polymer particles in a liquid".[8] The polymer in the particles may be organic or inorganic.[8] The IUPAC definition of "synthetic latex" is "latex obtained as a product of anemulsion, mini-emulsion, micro-emulsion, ordispersion polymerization".[8]
Thecells (laticifers) in which latex is found make up the laticiferous system, which can form in two very different ways. In many plants, the laticiferous system is formed from rows of cells laid down in themeristem of thestem orroot. Thecell walls between these cells are dissolved so that continuous tubes, called latex vessels, are formed. Since these vessels are made of many cells, they are known asarticulated laticifers. This method of formation is found in thepoppy family and in therubber trees (Para rubber tree, members of the familyEuphorbiaceae, members of themulberry and fig family, such as the Panama rubber treeCastilla elastica), and members of the familyAsteraceae. For instance,Parthenium argentatum the guayule plant, is in the tribeHeliantheae; other latex-bearing Asteraceae with articulated laticifers include members of theCichorieae, aclade whose members produce latex, some of them in commercially interesting amounts. This includesTaraxacum kok-saghyz, a species cultivated for latex production.[9]
In themilkweed andspurge families, on the other hand, the laticiferous system is formed quite differently. Early in the development of the seedling, latex cells differentiate, and as the plant grows these latex cells grow into a branching system extending throughout the plant. In manyeuphorbs, the entire structure is made from a single cell – this type of system is known as anon-articulated laticifer, to distinguish it from the multi-cellular structures discussed above. In the mature plant, the entire laticiferous system is descended from a single cell or group of cells present in theembryo.
The laticiferous system is present in all parts of the mature plant, including roots, stems,leaves, and sometimes thefruits. It is particularly noticeable in thecortical tissues. Latex is usually exuded as a white liquid, but is some cases it can be clear, yellow or red, as inCannabaceae.[2]
Latex is produced by 20,000flowering plant species from over 40families. These include bothdicots andmonocots. Latex has been found in 14 percent of tropical plant species, as well as six percent of temperate plant species.[10] Several members of the fungal kingdom also produce latex upon injury, such asLactarius deliciosus and othermilk-caps. This suggests it is the product ofconvergent evolution and has been selected for on many separate occasions.[2]
Latex functions to protect plants from herbivores and fungi from fungivores. The idea was first proposed in 1887 by Joseph F. James, who noted that latex ofmilkweed "carries with it at the same time such disagreeable properties that it becomes a better protection to the plant from enemies than all the thorns, prickles, or hairs that could be provided. In this plant, so copious and so distasteful has the sap become that it serves a most important purpose in its economy".[11] Evidence showing this defense function include the finding thatslugs will eat leaves drained of their latex but not intact ones, that many insects sever the veins carrying latex before they feed, and that the latex ofAsclepias humistrata (sandhillmilkweed) kills by trapping 30% of newly hatchedmonarch butterfly caterpillars.[2] This has also been found in fungi, with fewer arthropods infesting latex-producingLactarius than non-latex-producingRussula. In feeding experiments usingLactarius,Ambigolimax valentianus slugs avoid feeding on mushrooms that are exuding latex.[7]
Other evidence is that latex contains 50–1000× higher concentrations of defense substances than other plant tissues. Thesetoxins include ones that are also toxic to the plant and consist of a diverse range of chemicals that are either poisonous or "antinutritive."
Latex is actively moved to the area of injury; in the case ofCryptostegia grandiflora, latex more than 70 cm from the site of injury is mobilized.[2] The large hydrostatic pressure in this vine enables an extremely high flow rate of latex. In a 1935 report the botanistCatherine M. Bangham observed that "piercing the fruit stalk ofCryptostegia grandiflora produced a jet of latex over a meter long, and maintained [this jet] for several seconds."[12]
The clotting property of latex is functional in this defense since it limits wastage and its stickiness traps insects and their mouthparts.[2]
While there exist other explanations for the existence of latex including storage and movement of plant nutrients, waste, and maintenance of water balance that "[e]ssentially none of these functions remain credible and none have any empirical support".[2]
Natural rubber is the most important product obtained from latex; more than 12,000 plant species yield latex containing rubber, though in the vast majority of those species the rubber is not suitable for commercial use.[15] This latex is used to make many other products includingmattresses,gloves,swim caps,condoms,catheters andballoons.[16]
Latex is used in many types ofclothing. Worn on the body (or applied directly by painting), it tends to beskin-tight, producing a "second skin" effect.[18]
Synthetic latices are used incoatings (e.g., latex paint) andglues because they solidify bycoalescence of the polymer particles as the water evaporates. These synthetic latices therefore can form films without releasing potentially toxic organic solvents in the environment. Other uses include cement additives and to conceal information onscratchcards. Latex, usuallystyrene-based, is also used inimmunoassays.[19]
Others have a seriouslatex allergy, and exposure to latex products such aslatex gloves can causeanaphylactic shock.Guayule latex has only 2% of the levels of protein found inHevea latices, and it is being researched as a lower-allergen substitute.[21] Additionally, chemical processes may be employed to reduce the amount ofantigenic protein inHevea latex, yielding alternative materials such asVytex Natural Rubber Latex which provide significantly reduced exposure to latex allergens.
About half of people withspina bifida are also allergic to natural latex rubber. People who have had multiple surgeries and who have had prolonged exposure to natural latex are also more susceptible to a latex allergy.[22]
Many people with latex allergy also experience allergic reactions to certain fruits. This association has led to research regarding latex-fruit syndrome (LFS). This is a phenomenon characterized by cross-reactivity between natural latex rubber allergens and certain fruit allergens, leading to allergic reactions in sensitized individuals. It was described for the first time by Blanco et al. in 1994.[23]
In a 2024 comprehensive review by Gromek et al., the last 30 years of research on LFS were summarized, focusing on its prevalence, common cross-reactions, and clinical manifestations. The review found that the prevalence of LFS in latex-allergic patients varies widely, ranging from 4% to 88%, depending on diagnostic methods, geographical regions, and study populations. The most commonly implicated fruits in LFS include banana, avocado, kiwifruit, and papaya. Clinical manifestations are predominantly systemic, with 73% of hypersensitivity symptoms being systemic and 27% localized. Gromek et al. also highlighted the need for standardized diagnostic criteria and severity grading systems to improve the accuracy of LFS diagnosis and treatment.[24]
^Wang, Hui; Yang, Lijuan; Rempel, Garry L. (April 2013). "Homogeneous Hydrogenation Art of Nitrile Butadiene Rubber: A Review".Polymer Reviews.53 (2):192–239.doi:10.1080/15583724.2013.776586.S2CID96720306.
^Buttery, R. R.; Boatman, S. G. (1976). Kozlowski, T. T. (ed.).Water Deficits and Plant Growth, Volume IV: Soil Water Measurement, Plant Responses, and Breeding for Drought Resistance. Vol. IV (1st ed.). New York, New York 10003: Academic Press, Inc. p. 252.ISBN978-0124314269.{{cite book}}: CS1 maint: location (link)
^Morton, Maurice (2013).Rubber Technology (3rd ed.). Springer Science & Business Media.ISBN978-9401165342.{{cite book}}:Check|isbn= value: checksum (help)
^Mathews, Jennifer P. (2009).Chicle: The chewing gum of the Americas, from the ancient Maya to William Wrigley. Tucson: University of Arizona Press.ISBN978-0-8165-2821-9.
^Brunton, Laurence L. (2018).Goodman & Gilman's The Pharmacological Basis of Therapeutics. McGraw-Hill Education.ISBN978-1259585739.
^Kink and everyday life : interdisciplinary reflections on practice and portrayal. Kylo-Patrick R. Hart, Teresa Cutler-Broyles. Bingley. 2021.ISBN978-1-83982-918-5.OCLC1262726608.{{cite book}}: CS1 maint: location missing publisher (link) CS1 maint: others (link)
^Blanco, C.; Carrillo, T.; Castillo, R.; Quiralte, J.; Cuevas, M. (October 1994). "Latex allergy: clinical features and cross-reactivity with fruits".Annals of Allergy.73 (4):309–314.ISSN0003-4738.PMID7943998.
