Resins are complex, lipid-soluble mixtures of various compounds. Usually, a resin is made up of a diterpenoid-and triterpenoid-containing nonvolatile fraction, as well as a volatile fraction. In the more common terpenoid resins, monoterpenoids and sesquiterpenoids predominate in the volatile fraction. Oleoresins are resins that contain a particularly high terpenoid volatile fraction, making them particularly fluid. In the less common phenolic resins, hydrophobic flavonoids and phenyl-propanoids predominate. Resins are usually secreted by specialized structures in woody angiosperms. All resins are sticky and harden when exposed to the air. They produce fragrant smoke when burned and thus are commonly used as incense (frankincense and myrrh are resins used for this purpose). Amber is fossilized resin. Balsams are highly fragrant resins that tend to stay relatively soft at room temperature.

Gums and mucilages are not resins but instead are thick, sticky mixtures of polysaccharides. Sometimes, gums and resins intermix to form gum resins, but these are formed separately and are chemically distinct. Latex is also not a resin but is instead an even more complex chemical mixture produced by distinct secretory tissues within the plant that are separate from resins.

It is not surprising that given their diverse chemical makeup, the medicinal actions of resins vary enormously. Generally speaking, most resins are antimicrobial and wound healing in animals and in the plants that secrete them. This has been shown, for example, with balsam of Peru, the resin of Myroxylon balsamum var. perierae. Balsam of Peru also speeds healing of radiation burns when applied topically. Topical application of pine resin to wounds and burns has been shown to stimulate local immune function, normalize wound hemodynamics, and stimulate squamous epithelialization. Beyond this, resins from different plants can have a wide array of effects. For example, frankincense, the gum resin of Boswellia serrata, is well documented as an inflammation modulator that is helpful in asthma and ulcerative colitis; this is attributed at least in part to its inhibition of 5-lipoxygenase. The gum resin of Commiphora molmol (myrrh) is antiparasitic, analgesic, and antineoplastic. Resins also find widespread use outside of medicine as varnishes, lacquers, waterproofing agents, adhesives, and precursor materials for industrial chemical production.

Select Resin-Rich Herbs
Abies spp (fir)
Boswellia serrata (frankincense)
Bursera microphylla (elephant tree)
Cannabis sativa (marijuana)
Commiphora molmol (myrrh)
Commiphora mukul (guggul)
Dryopteris fillix-mas (male fern)
Grindelia spp (gumweed)
Larrea tridentata (chaparral)
Pinus spp (pine)
Pistachio lentiscus (mastic)
Zingiber officinale (ginger)

Resins are generally safe (Select Resin-Rich Herbs). Contact allergy to balsams is relatively common. In one series, roughly 1 in 100 human patients patch-tested positive to tincture of benzoin, with 1 in 400 having an intense reaction. More problematic are the resins of the Anarcardiaceae family, such as the all-too-familiar Toxicodendron radicans (poison ivy), which can cause severe type 4 hypersensitivity reactions in susceptible animals.