The Golden Spice : Yaingang in sunscreens

Dr Sophy A Shimray / Dr Francis AS Chipem *

Yaingang (Turmeric Roots) as seen at Lamlong Keithel in September 2016 :: Pix - Shankar Khangembam

Self-care has become a significant part of our daily lives, with skincare playing a central role. As the world progresses in cosmetics, thousands of skin care products are available,from brightening and anti-aging creams to acne scar treatments and pigmentation correctors. However, one product remains non-negotiable : sunscreen.

Regardless of the skincare routine, sunscreen protects the skin from ultraviolet (UV) rays or radiation and prevents premature aging. No skincare routine is complete without sunscreen, which serves both as an aesthetically appealing factor and an effective and photo stable UV filter.

Excessive exposure to UV radiation from the sun causes damaging effects, including tanning, sunburn, DNA mutations, and photo aging in humans. Based on the wavelength or frequency of the radiation, UV radiation can be categorized into UVA (315-400 nm), UVB (280-315 nm), and UVC (100-280 nm) in increasing order of energy carried by the radiation.

UVC ray, generally known as hard UV, is absorbed by the atmosphere, particularly the ozone layer, and therefore do not reach the surface of the Earth. The major concern rendered on human skin by sunlight is the exposure to UVA and UVB radiations, particularly the UVA rays or the soft UV, as the ozone layer partly absorbs UVB rays before reaching the Earth’s surface.

As mentioned above, in addition to ingredients meant for beautification, a sunscreen's major and active components are UV filters that filter off or absorb UV radiation. Based on the nature and method of protection from radiation, sunscreens are broadly categorized into mineral and chemical sunscreens. Widely used mineral ingredients in commercial sunscreens are zinc oxide and titanium dioxide.

Mineral sunscreens remain on the outer layer of the skin and function as a barrier, whereas chemical sunscreens penetrate the skin and perform more like an absorbent. Chemical sunscreens are lightweight and quickly absorbed into the skin, making them a popular daily choice.

However, commonly found components in commercial sunscreens, such as avobenzone, oxybenzone, homosalate, meldrum derivatives, and octinoxate, have sparked environmental concerns because of toxicity in their development and their possible contribution to coral bleaching and other disruptions to marine ecosystems, raising significant ecological issues. Additionally, some people experience skin irritation and allergic reactions due to certain chemical filters.

Another demerit is that certain chemical compounds may break down when exposed to sunlight, reducing their effectiveness unless paired with stabilizing ingredients. In contrast, mineral sunscreens use natural components such as zinc oxide and titanium dioxide, which remain on the skin’s surface to reflect the UV rays.

These sunscreens provide instant protection and are usually mild on the skin, making them an excellent choice for individuals with sensitive skin. However, they sometimes feel heavy, leaving a white cast on the skin.

With the growth in cosmetics industries, there is an increasing interest in natural, effective, and eco-friendly skincare products. More individuals are becoming aware of their skincare ingredients and leaning towards natural and “organic” options instead of synthetic chemicals. This has led to increased interest in naturally derived sunscreen ingredients.

Historically found as a practice particularly in South India, turmeric pastes are applied as thin coatings on faces for protection from direct exposure to sunlight. Turmeric, derived from the root of the Curcuma longa plant, is widely used in Indian, Southeast Asian, and Middle Eastern cuisines, giving curry its vibrant yellow colour.

Beyond the kitchen, turmeric has a rich history in traditional medicine, particularly in Ayurveda and traditional Chinese medicine, for its healing and therapeutic properties. Turmeric, locally known in Manipur as “yaingang”, is valued for its anti-inflammatory, antioxidant, and antimicrobial benefits.

As the general public becomes more aware and health conscious, numerous sunscreen products have started introducing naturally available and organic turmeric as ingredients, replacing those synthetic chemicals and thus reviving the old practice. The key to turmeric’s protective power lies in a group of bioactive compounds called curcuminoids, constituting 1-9% of the contents.

Depending on the substituents in the molecular structure of the curcuminoid, it can be curcumin, demetho-xycur-cumin, or bisdemethoxycur- cumin. These compounds are polyphenolic compounds, which render their bright colour and medicinal properties.

Structurally, curcuminoid molecules have aliphatic chains containing seven carbon atoms linking two phenol rings at the two ends by five carbon-carbon single and three carbon-carbon double bonds, which play a vital role in the dissipation of absorbed UV energy/radiations in a non-radiative manner. Rotating a carbon-carbon single about the bond as an axis result in interconversion between rotamers (s-cis and s-trans).

In contrast,the rotation of a carbon-carbon double about the bond axis results in interconversion between geometrical isomers (cis/Z and trans/E configurations). A recent computational study published in Spectrochimica Acta Part A (doi: j.saa.2023.123449) reported about quantum chemical calculations under the formulation of density functional theory, which suggest that the curcuminoid molecules undergo carbon-carbon single bond rotation, leading to the population distribution of a single geometrical isomer into sixteen different rotamers of minor energy differences and small barrier for interconversion.

For instance, in one Z1E2E3 configuration of bisdemethoxy curcumin, the sixteen rotamers lie within a small energy window of 3.087 kcal/mol, which indicates that the population of each rotamer, predicted by Boltzmann distribution, is significant.

Further, each compound can undergo carbon-carbon double bond rotation, leading to eight configurations. Simulations of radiation absorption by these structures show maximum absorbance falling within the range of 300-400 nm, which comfortably can be said within the UVA region and is comparable with the experimental values.

After energy absorption in the form of radiation, the interconversion between rotamers is further enhanced. In contrast, the interconversion between geometrical isomers passes through a nonradiative decay pathway called conical intersection or avoided crossing. Both these processes dissipate the absorbed radiation nonradiatively, thus filtering the UV rays before reaching/penetrating and damaging the skin.

Further, these compounds have cyclic intramolecular hydrogen-bonded ring in the middle of the structure, which creates a favorable condition to undergo another light-initiated process called excited state intramolecular proton transfer. This process also acts as another pathway for the dissipation of the absorbed UV rays, in addition to the two processes.

The attraction of these processes in these compounds is that these UV filters are “recycled” through these processes, without breaking down or undergoing harmful reactions. This is crucial because many chemical sunscreen ingredients degrade under UV exposure, reducing their effectiveness over time.

Curcuminoids, however, can shift between different structural forms while always returning to their original structure, ensuring long-term stability under sunlight. This makes them a reliable and durable option for sun protection.

Besides, turmeric-based sunscreens offer extra therapeutic benefits as curcuminoids are potent antioxidants and anti-inflammatory agents, thus protecting the skin from oxidative stress caused by sun exposure and reducing inflammation.

Furthermore, turmeric, in appropriate combination mainly with citrus fruits, produces a pleasant aroma, which has now become an essential ingredient in numerous cosmetics. As research continues, turmeric-based sunscreens could become a game-changer in the skincare industry, providing practical, natural, and holistic sun protection.


This article is written as part of the scientific social responsibility under a research project funded by the Anusandhan National Research Foundation, Government of India (EEQ/2022/000578).