Commonly known as neem or nimba, Azadirachta indica traditionally has been used as an oil or poultice to lighten skin pigment and reduce joint inflammation. Neem is a drought-resistant evergreen tree with thin serrated leaves, white fragrant flowers, and olivelike fruit (Figure 1). This plant is indigenous to India but also is readily found within tropical and semitropical environments throughout the Middle East, Southeast Asia, North Africa, and Australia.
FIGURE 1. Leaves of a neem plant (Azadirachta indica).
Traditional Uses
For more than 4000 years, neem leaves, bark, fruit, and seeds have been used in food, insecticide, and herbal medicine cross-culturally in Indian Ayurvedic medicine and across Southeast Asia, particularly in Cambodia, Laos, Thailand, Myanmar, and Vietnam.1-3 Because of its many essential nutrients—oleic acid, palmitic acid, stearic acid, linoleic acid, behenic acid, arachidic acid, and palmitoleic acid—and readily available nature, some ethnic groups include neem in their diet.4 Neem commonly is used as a seasoning in soups and rice, eaten as a cooked vegetable, infused into teas and tonics, and pickled with other spices.5
All parts of the neem tree—both externally and internally—have been utilized in traditional medicine for the treatment of various diseases and ailments. The flowers have been used to treat eye diseases and dyspepsia, the fruit has been employed as an anthelmintic, the seeds and leaves have been used for malaria treatment and insecticide, the stem bark has been used for the treatment of diarrhea, and the root bark has been used for skin diseases and inflammation.6 Neem oil is a yellow-brown bitter substance that often is utilized to treat skin diseases such as psoriasis, eczema, fungal infections, and abscesses.
Case Report—A 77-year-old man presented with a diffuse rash across the lower back. He reported that he had been using topical neem oil to alleviate lower back pain and arthritis for the last 6 months with noted relief and improvement of back pain. After roughly 3 to 4 months of using neem oil, he noted a rash on the lower back, bilateral flanks, and buttocks (Figure 2). The rash was asymptomatic, and he denied any pruritus, scaling, pain, or burning. The patient was referred to dermatology and received a diagnosis of chemical leukoderma secondary to contact with A indica. The patient was advised to stop using the topical neem oil, and the rash was simply monitored, as it was asymptomatic.
FIGURE 2. Hypopigmentation on the lower back, bilateral flanks, and buttocks due to neem oil–induced chemical leukoderma.
Bioactivity
Research has elucidated multiple bioactivity mechanisms of neem, including melanogenesis-inhibitory activity, toxicity against pests, antimalarial activity, and antioxidant activity.1,7-9 Literature on the diverse phytochemical components of A indica indicate high levels of limonoids, flavonoids, and triterpenoids that are responsible for much of its antioxidant, anti-inflammatory, and insecticide properties.1,10
Melanogenesis-Inhibitory Activity—To date, neem has been added to a number of cosmetic products used in Ayurvedic medicine. One study of isolated compounds in A indica showed superior inhibitory activities against melanogenesis with minimal toxicity to cells (86.5%–105.1% cell viability). Western blot analysis of samples extracted and isolated from neem root and bark showed melanogenesis-inhibitory activities in B16 melanoma cells through the inhibition of microphthalmia-associated transcription factor expression and decreased expression of tyrosinase, as well as tyrosinase-related proteins 1 and 2, which are largely responsible for melanin synthesis.11 In another study, A indica flowers and their extracted constituents—6-deacetylnimbin and kaempferide—suggest melanogenesis-inhibitory activities in B16 melanoma cells with little to no toxicity to the cells (81.0%–111.7% cell viability).1 In an evaluationof A indica seed extracts, some of the isolated limonoids and diterpenoids exhibited a marked melanogenesis-inhibitory effect (74%–91% reduction of melanin content) with no toxicity to the cell.5 All of these studies indicate that active compounds in neem root, bark, flowers, and seeds may be potential skin-lightening agents.
Toxicity Against Pests—Neem seeds have phytochemicals that convey some insecticidal properties. The seeds often are ground into a powder, combined with water, and sprayed onto crops to act as an insecticide. As a natural method of nonpesticidal management, A indica acts as an antifeedant, insect repellent, and egg-laying deterrent that protects crops from damage. Studies of A indica have noted effective nonpesticidal management against arthropod pests such as armyworm, termites, and the oriental fruit fly.7,12,13