The primary purpose of the skin is protection; it provides a physical barrier against radiation, toxic chemicals, and water exposure to protect the internal organs. In carrying out this function, the skin encounters inevitable harm which leads to the signs of skin ageing that we are familiar with: wrinkles, fine lines, altered pigmentation, loss of volume and skin tone. We know that both internal and external factors lead to skin ageing; internal factors include smoking and excess alcohol, and external factors include sun exposure through UV radiation and environmental pollution. I have come across many different theories of how exposure to pollution can lead to skin ageing. The most widely accepted is the theory of free radicals and oxidative stress. This states that the accumulation of free radical damage and oxidative stress creates a cascade of intracellular damage, which impairs cellular processes that allow skin cells to divide in order to grow and repair themselves.1,2
Oxidative stress and free radical theory
It is commonly accepted that UV radiation and photoageing cause the majority of visible signs of ageing. When UV radiation comes into contact with the skin surface it initiates the production of free radicals and the formation of reactive oxidative species (ROS).3 Examples of these are oxygen ions, free radicals and peroxides. ROS are highly reactive, unstable molecules due to the presence of their unpaired electron. They will attach themselves to anything from a lipid membrane to the DNA in a cell’s nucleus, in an attempt to steal the last electron needed to stabilise themselves. This process causes intracellular chaos. The damage causes inflammation, led by cytokine generation, which not only affects the cell itself, it over-spills into surrounding structures, causing collateral damage of the tissue.3
Activation of matrix metalloproteinases
UV exposure also activates destructive intracellular enzymes, known as matrix metalloproteinases (MMPs). This group of enzymes includes collagenase, which cause the breakdown of collagen and elastin. In a different context, the activation of MMPs is essential for the remodelling of connective tissue and wound healing. However, when UV radiation and toxic pollutants artificially trigger this process, it causes premature collagen breakdown, which leads to accelerated ageing of skin cells, and ultimately the visible signs of ageing, in particular, wrinkle formation and volume loss.4
Chemical pollutants
UV radiation is not the only environmental factor that causes skin ageing. A landmark study in the Journal of Investigative Dermatology compared women living in urban and rural environments over 24 years and found that those living in the urban area that had been exposed to increased pollution had more dark spots and wrinkling.5
Microscopic particles are released into the atmosphere every second from fires, power plants, construction sites and motor vehicles. These tiny chemical particles create an invisible but toxic film on the surface of the skin.6 The microscopic size of the particles allows them to easily penetrate the skin pores, making their way through the deeper layers of the skin to eventually target the skin cell nucleus. They create a cascade of intracellular damage. This process is driven by the activation of free radicals leading to oxidative stress and the activation of MMP, both described above.5
It also triggers a phenomenon known as replicative senescence; this is a process of cellular ageing, where the cell can no longer replicate. This is a natural process but it can be triggered prematurely by the effects of UV radiation and environmental toxins. The hallmark of this process is the shortening of telomeres at the ends of DNA strands, which help ensure chromosomal stability. Skin cells are some of the most rapidly dividing cells in the body; when DNA is damaged, it is susceptible to replicative senescence, which means they are no longer able to divide, multiply and repair themselves.5
The additive effect of these processes leads to intracellular and collateral inflammation and dehydration of skin cells and surrounding structures. This causes collagen breakdown and damages the lipid layer of the skin, thus impairing its barrier function, which manifests itself in the loss of elasticity, firmness and volume.7
Ozone effects
The ozone also has an impact on skin ageing and can trigger exacerbations of pre-existing skin conditions.8 The ozone exists in the stratosphere and troposphere and is also found in low concentrations at ground level as a by-product of human activities, which release chemical pollutants into the atmosphere, such as smog. The effects of the ozone are amplified by the presence of other environmental factors such as UV radiation and other toxic pollutants.8
Studies suggest that the ozone, like other chemical pollutants, first targets the stratum corneum and start to penetrate down to the dermis. Their path of destruction is driven by oxidative stress, the formation of free radicals and MMP activation.8
The presence of the ozone induces epidermal damage to the skin through collagen breakdown and impairing the lipid membrane of skin cells to inhibit their barrier function. In addition, the ozone also inhibits the protecting effects of antioxidants, making harmful damage inevitable and irreversible once the process has started. The inflammatory aspect of ozone damage has been associated with a flare-up in skin conditions including; urticaria, eczema, contact dermatitis, and other nonspecific eruptions.9,10,11
Skin conditions triggered by pollution
In addition to premature ageing, what ailments can pollution trigger in the skin?
Chloracne
Acne and the effects of acne are something that most practitioners are familiar with. On rare occasions, environmental pollution can result in an acne variant called chloracne, also known as halogen acne. Chloracne results from environmental exposure to certain halogenated aromatic hydrocarbons. The skin’s manifestations of acne indicate systemic poisoning by these compounds.12 Von Bettman first observed chloracne in 1897, followed by Herxheimer in 1899.12 Today, chloracnegens are thought to include polychlorinated compounds, such as herbicides. Chloracne is caused by direct contact of the toxins with the skin, however some cases have been documented which involve ingestion or inhalation of toxins too.13 Although chloracne tends to slowly resolve upon cessation of exposure to chloracnegenic compounds, the duration of chloracne correlates with the severity of the disease.13 Like other causes of acne, chloracne can be challenging to treat. The most effective documented treatment is topical treatment with retinoids.14
Irritant contact dermatitis
The direct effect of toxic chemicals on the skin surface can lead to an eczematous eruption. Commonly this condition is caused by cosmetic products or a change in washing powder, for example, but it can also be triggered by toxins and solvent in the atmosphere.15
Chemical depigmentation
Exposure to environmental chemicals can also have a destructive effect on epidermal melanocytes, which can cause hyper or hypopigmentation of the skin known as chemical depigmentation, which resembles vitiligo. The most common causative agents are derivatives of hydroquinone and related compounds.16 Occupational leukoderma is commonly observed, where chemicals have a depigmenting effect on the skin, which is typical in workers who have skin contact with them. This condition tends to have a hypopigmenting effect on the skin called chemical leukoderma, which unfortunately has no specific treatment.16
Recognising the signs
The signs of accelerated skin ageing caused by pollution are similar to those we are all aware of. When caused by environmental exposure to UV, in combination with toxic chemicals, the skin signs tend to show changes in skin texture and pigmentation, rather than the formation of lines, wrinkles and volume loss alone. The signs of skin ageing, secondary to UV radiation and environmental pollutants, are also often associated with inflammatory changes in the skin, and the flare up in existing or new skin conditions such as acne and dermatitis.
History
When assessing patients it’s key to talk thorough their history, in particular occupational history, their sun exposure and exposure to chemicals or toxins. In patients with pre-existing skin conditions such as eczema, acne or dermatitis, ask about triggering and relieving factors, to see if a pattern emerges in association with environmental changes, i.e. do symptoms only flare up at work? Are they seasonal? Are they triggered by the use of particular cosmetic products?
Examination
Carry out a full facial assessment, paying attention to patterns of wrinkle formation and volume loss, and ask yourself: are they localised or global? Are they associated with hyper/ hypopigmentation? How is the skin texture? Does this pattern extend into the neck? Is the extent of the ageing consistent with the age of the patient? It is also useful to examine the patient’s hands too, rather than just focusing on the face, as hands and face are often the main areas suffering repeated exposure to the effects of the environmental pollutants.
Management
Antioxidants
Antioxidants prevent against free radical damage and oxidative stress through stabilising the free radicals by donating one of their own electrons to neutralise them and ending the ‘electron stealing’ reaction. This ends the path of destruction in the skin cell nucleus, which can lead to inflammation and collagen damage.17
Antioxidants can be applied to the skin directly, in the form of creams or serums, or can be obtained from dietary sources. Vitamin E is the most abundant fat-soluble vitamin in the body and defends against oxidation and lipid peroxidation.18
Vitamin C is a water-soluble antioxidant, which acts primarily in cellular fluid. It also helps to return vitamin E to its natural form. Topical preparations need to be able to penetrate the outmost barriers of the skin’s surface in order to reach the cell nucleus to have the desired effect.19 The dietary effects of antioxidants are controversial; as little as 1% of antioxidants taken orally reaches the surface skin where they are needed to carry out their protective role.19 That said, a diet rich in antioxidants should always be encouraged as their benefits are not exclusive to skin; research shows antioxidants have other health benefits, in particular protecting against cardiovascular disease and cancer.20
Cleanse
Thoroughly cleansing the skin surface to remove the invisible film of toxic pollutants gathered over the day is the first step in protection. Cleansing and exfoliating with products containing alpha hydroxy acids (AHA) like glycolic acid, are excellent as they to help to chemically exfoliate the skin and encourage new skin cells to the skin surface.
Protect
Sunscreen is fundamental to protecting the skin from harmful UV rays. It provides a physical barrier to prevent UV radiation coming into contact with the skin, which creates the harmful free radical cascade. SPF 50 is recommended for complete protection. It should be used separately as the final part of the skincare regime, and not combined with moisturisers and foundations, as they are less effective.
High factor sunscreen is especially important when using products containing AHAs as they increase the photosensitivity of the skin.
Summary
UV radiation, ozone and chemical pollutants can all cause premature skin ageing by the activation of free radicals and matrix metalloproteinases, and oxidative stress. This leads to intracellular inflammation and the breakdown of collagen and elastin. Damage can be minimised by effective cleansing, application of antioxidants and, most importantly, application of sunscreen.
