There are four main species of Boswellia that produce true frankincense. Resin from each of the four is available in various grades. The grades depend on the time of harvesting; the resin is hand-sorted for quality.

Frankincense is tapped from the scraggy but hardy trees by slashing the bark, which is called striping, and allowing the exuded resin to bleed out and harden. These hardened resins are called tears. There are several species and varieties of frankincense trees, each producing a slightly different type of resin. Differences in soil and climate create even more diversity of the resin, even within the same species. Boswellia sacra trees are considered unusual for their ability to grow in environments so unforgiving that they sometimes grow out of solid rock. The initial means of attachment to the rock is unknown, but is accomplished by a bulbous disk-like swelling of the trunk. This growth prevents it from being ripped from the rock during violent storms. This feature is slight or absent in trees grown in rocky soil or gravel. The trees start producing resin when they are about eight to 10 years old.^[2] Tapping is done two to three times a year with the final taps producing the best tears due to their higher aromatic terpene, sesquiterpene and diterpene content. Generally speaking, the more opaque resins are the best quality. Fine resin is produced in Somalia, from which the Roman Catholic Church purchases most of its stock.^[3]

Recent studies have indicated that frankincense tree populations are declining, partly due to over-exploitation.^[4] Heavily tapped trees produce seeds that germinate at only 16% while seeds of trees that had not been tapped germinate at more than 80%. In addition, burning, grazing, and attacks by the longhorn beetle have reduced the tree population.^[5] Conversion (clearing) of frankincense woodlands to agriculture is also a major threat.^[6]

Frankincense resin is edible and is used in traditional medicines in Africa and Asia for digestion and healthy skin. For internal consumption, it is recommended that frankincense be translucent, with no black or brown impurities. It is often light yellow with a (very) slight greenish tint. It is often chewed like gum, but it is stickier.

In Ayurvedic medicine frankincense (Boswellia serrata), commonly referred to in India as "dhoop," has been used for hundreds of years for treating arthritis, healing wounds, strengthening the female hormone system and purifying the air. The use of frankincense in Ayurveda is called "dhoopan". In Somali, Ethiopian, Arabian, and Indian cultures, it is suggested that burning frankincense daily in the house brings good health.^[18]

For therapy trials in ulcerative colitis, asthma and rheumatoid arthritis there are only isolated reports and pilot studies from which there is not yet sufficient evidence of safety and efficacy. Similarly, the long-term effects and side effects of taking frankincense has not yet been scientifically investigated. Nonetheless, several preliminary studies have been published.

A 2008 study reported that frankincense smoke was a psychoactive drug that relieves depression and anxiety in mice.^[23][24] The researchers found that the chemical compound incensole acetate^[25] was responsible for the effects.^[23]

In a different study, an enriched extract of "Indian Frankincense" (usually Boswellia serrata) was used in a randomized, double-blinded, placebo-controlled study of patients with osteoarthritis. Patients receiving the extract showed significant improvement in their arthritis in as little as seven days. The compound caused no major adverse effects and, according to the study authors, is safe for human consumption and long-term use.^[26]

In a study published in 2009, it was reported that "Frankincense oil appears to distinguish cancerous from normal bladder cells and suppress cancer cell viability."^[27]

A 2012 study in healthy volunteers determined that exposure to 11-keto-β-boswellic acid (KBA), a lead boswellic acid in the novel solubilized frankincense extract Boswelan, is increased when taken with food. However, simulations based on a two-compartment pharmacokinetic model with single first-order absorption phase proposed that the observed food interaction loses its relevance for the simulated repeated-dose scenario.^[28]

In a 2012 study, researchers found that the "behavioral effect [of insensole actetate] was concomitant to reduced serum corticosterone levels, dose-dependent down-regulation of corticotropin releasing factor and up-regulation of brain derived neurotrophic factor transcripts IV and VI expression in the hippocampus. These data suggest that IA modulates the hypothalamic–pituitary–adrenal (HPA) axis and influences hippocampal gene expression, leading to beneficial behavioral effects supporting its potential as a novel treatment of depressive-like disorders."^[29]

In study published in 2014, researchers found "the effects of frankincense and sandalwood essential oils on J82 cells and UROtsa cells involved different mechanisms leading to cancer cell death. While frankincense essential oil elicited selective cancer cell death via NRF-2-mediated oxidative stress, sandalwood essential oil induced non-selective cell death via DNA damage and cell cycle arrest."^[30]