Our skin protects against trauma and bacterial invasion, prevents dehydration, regulates body temperature, and provides the ability to sense temperature and touch.
The outmost epidermis and the associated stratum corneum form a waterproof barrier and contain pigment‐producing melanocytes.
The next layer, the dermis, contains fibrous and elastic tissues, hair follicles, nerve fibers, and sweat glands. The fibrous and elastic tissues provide skin its strength and flexibility.
Under the dermis is a layer of subcutaneous fat and connective tissues. Without proper preventative measures, environmental factors such as sunlight and air pollution will damage the skin, resulting in various signs of premature skin ageing.
Premature skin ageing can arise from exposure to many environmental factors such as ultraviolet (UV) radiation, high‐energy visible (HEV) light in the blue spectrum, infrared radiation, and environmental pollution.
These extrinsic factors cause the generation of reactive oxygen species (ROS) which initiate photoageing and DNA damage. DNA damage often causes skin cancers.
Novel skin protection strategies targeting a variety of environmental and energy aggressors, including UV radiation, HEV light in the blue spectrum, and infrared radiation, can be formulated by taking a page out of nature’s book.
Plants produce powerful molecules with robust energy absorbing abilities as well as effective mediation abilities against oxidation stresses and pollution stresses.
Identifying the right plant components and sustainably harnessing these functional phyto-compounds for skin protection purposes presents vast opportunities for the skincare industry.
All plants have antioxidant potential. This is because chloroplasts and mitochondria are the two main sites of ROS generation in plant cells.
ROS are also involved in maintaining a fine balance between energy linked functions and the level of ROS generation. Within the plant cell, ROS generation occurs mainly at photosystem I and II (PS I and PS II) of the chloroplasts, as well as complex I, ubiquinone, and complex III of the mitochondrial electron transport chain (ETC).
Under normal physiological conditions, there are electron slippages from PS I and PS II of the chloroplasts and the membrane of the mitochondrial ETC. These electrons later react with molecular oxygen to produce ROS.
Reactive nitrogen species (RNS) are also formed in various compartments of the cell, including the chloroplasts and mitochondria. These free radicals are constantly produced in the subcellular organelles of living cells.
Most of the time, the production of free radicals is genetically planned since they function as signalling molecules.
However, overproduction of free radicals can happen and damage biomolecules such as DNA, proteins, and lipids. Plants have efficient enzymatic and non-enzymatic antioxidant defence systems to avoid the toxic effects of free radicals.
The enzymatic systems include SOD, catalase (CAT), and glutathione reductase (GR). The non-enzymatic systems consist of low molecular weight antioxidants such as ascorbic acid, glutathione, proline, carotenoids, phenolic acids, flavonoids, etc., and high molecular weight secondary metabolites such as tannins.
There are two main reasons for the synthesis and accumulation of these non-enzymatic antioxidants by plants.
First, the genetic makeup of plants imparts them with an innate ability to synthesize a wide variety of phytochemicals to perform their normal physiological functions or protect themselves from herbivores and microbial pathogens.
Another reason for the synthesis of these phytochemicals is the natural tendency of plants to respond to environmental stress conditions.
Plants synthesize low molecular weight antioxidants as redox buffers to interact with numerous cellular components and to influence plant growth and development.
This is achieved by modulating processes from mitosis and cell elongation to senescence and death.
Plants also synthesize and accumulate a range of low and high molecular weight secondary metabolites. These secondary metabolites play important roles in ROS metabolism and avoiding uncontrolled oxidation of essential biomolecules.
Under normal physiological conditions, increases in free radical production are relatively small.
Common housekeeping antioxidant capacity is sufficient to maintain redox homeostasis.
However, the metabolic pathways of plants are sensitive to abiotic and biotic stress conditions such as high light intensity, heat, drought, anoxic conditions, and pathogen attack.
It is known that there is an approximately 3-to-10-fold increase in free radical production under stress conditions.
Some secondary antioxidant metabolites occur constitutively, while others are formed in response to biotic and abiotic stresses; the accumulation of phenolic compounds and enhancement of phenylpropanoid metabolism were observed under different environmental stress conditions.
For example, synthesis of flavonoids is known to be induced by UV stress, heavy metals toxicity, or low temperature and low nutrient conditions. This might explain flavonoids’ UV-absorbing, radical scavenging, and metal-chelating abilities.
UVB radiation was found to affect the production of various high molecular secondary metabolites such as tannins and lignin. In addition, plants growing in tropical and high-altitude conditions have been shown to contain a higher level of flavonoids than those growing in temperate conditions, likely due to an overexposure to light or UV radiation.
By thoroughly understanding the mechanisms of plant antioxidant generation, we can identify the correct plant or plant parts from which efficacious molecules can be harvested to provide both light shielding and radical- or pollutant-mediation functionalities.
The fundamental causes of plant antioxidant formation give us clues on where to search for these species; we must also research suitable ways to acquire these molecules sustainably and present them at a meaningful level to the skincare industry.
This is the key first step to achieving effective, natural skin protection.
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