A sunscreen from bark
For over 2,000 years, people in Myanmar have applied a yellowish-white paste called Thanaka to their skin for cosmetic and medicinal purposes. This paste is a cultural practice and a functional sunscreen derived from nature. The primary source of Thanaka is the bark of the Hesperethusa crenulata tree (also known as Limonia acidissima), which thrives in the arid, central region of the country. The area around Pakokku in the Magway Region is a major cultivation centers for high-quality Thanaka trees.
The traditional preparation is a simple, manual process. Bark or wood from the Thanaka tree is ground against a circular stone slab, called a kyauk pyin, with a small amount of water. This action creates the fine, fragrant paste that is then applied to the face, often in simple circular patches on the cheeks or in more elaborate, leaf-like designs. The practice is common among all ages and genders, used both for its skin-cooling properties in the hot climate and for sun protection.
The trees themselves require patience from the cultivators. While some trees can be harvested after seven years, the highest-quality bark is said to come from trees that have matured for at least 35 years. This slow growth contributes to the value placed on potent Thanaka. The plantations in Pakokku are part of a long-standing agricultural tradition that directly supports a cultural institution.
The chemistry of protection
Scientific analysis of Thanaka bark has identified the chemicals behind its long-held reputation as a sun protectant. The primary active ingredient responsible for its UV-blocking capability is a furanocoumarin compound called marmesin. Chemical analysis shows that marmesin's molecular structure is highly effective at absorbing ultraviolet radiation, particularly in the UVA spectrum, with a maximum absorption (λmax) at 335 nanometers. Its efficacy in absorbing UVA has been compared to that of titanium dioxide.
Phytochemical studies have also isolated a range of other bioactive compounds from Hesperethusa crenulata bark. These include other coumarins, flavonoids, tannins, and phenolic compounds. These substances contribute additional benefits. For instance, studies show Thanaka extracts have strong antioxidant and significant anti-inflammatory properties. The antioxidant activity helps to scavenge free radicals, which is a factor in preventing skin aging.
Research also indicates that the paste has mild tyrosinase inhibition activity, which relates to its traditional use for skin lightening, as tyrosinase is an enzyme involved in melanin production. The presence of these multiple active compounds shows that the traditional use of Thanaka is grounded in verifiable science, where a single natural source provides photoprotection, anti-inflammatory, and antioxidant effects.