Social distancing in the time of COVID-19 has imposed significant restrictions on all our activities, including social contact and mobility. We are palpably aware of the risk of infection whether through touching a surface or via close contact with another person. As a result, significant shifts in consumer behaviour have been observed in terms of hygiene. Increased hand washing, sanitation, and wider cleaning is potentially leading to changes in the hand’s skin microbiome and deterioration of the skin’s condition (more on this here).
But what effect does limited social contact and increased hygiene have on our skin microbiome? And has the adverse impact of COVID-19 on our mental health introduced other changes?
We’re in this together: the household microbiome & the microbial exchange
While Covid-19 restrictions vary from country to country, there’s no doubt that our worlds have quickly become smaller and activities limited. Quite simply, more time is spent at home. Our specific household ‘bubbles’ dictate the collective microbiome in the environment in which we now live.
Research into the microbiome of airplane cabins found that bacterial communities are specific to the individual airplane, derived from human skin and oral commensal bacteria as well as environmental bacteria (1). Likewise, at home people, objects and environmental bacteria together make up the home’s unique, collective microbiome.
Every person carries a personal skin microbiome, unique but also dynamic in interaction with an environment consisting of people and personal accessories, such as our shoes, clothing (more on that here!) and phones. Phones touching our faces and hands serve as a potential source and sink for our own skin microbiome, while our shoes act as a carrier, bringing microbes from soil and the external environment into the home (2).
Our skin microbiomes are also shaped by the people we live with. Those closest to us affect us most. For example, a child’s skin microbiome, which helps the development of the body’s immune system, is more like the mother’s microbiome than a microbiome of an unrelated woman (3). Similarly, cohabiting couples share more of their microbiota than people from different households.
The spread and sharing of microbes is further boosted by owning a pet (4). People spending more time at home, as is the case for many at the moment, means the home microbiome environment is likely to remain less challenged. Learning from studies around microbial exchange in contact sports, less contact limits the amount of colonization by opportunistic bacterial species (5).
Conserving the ‘family bubble’ could potentially increase protective features of the human body by limiting the acquisition of transient pathogenic flora. Conversely, pathogens acquired from diseased pets or other brought-in infections can have a negative impact. The net result is yet to be seen, however, as there are still many unknowns around the new and unusual circumstances under which we’re living, and a microbial challenge can be good for the skin microbiome.
Mental health and the gut-brain-skin axis
The impact of isolation on mental health
Beyond the physical impact of disconnection, being required to distance from others – as most of us have been -can lead to feelings of sadness, hopelessness, and isolation. Regardless of the likely necessity of lockdown, six months into the COVID-19 pandemic, the increase in stress, anxiety and depression is widely reported, often with added burnout for essential workers, leaving the population feeling emotionally drained (6).
De-personalization, fear of uncertainty, lack of touch and lack of displayed positive emotions – due to face coverings – all carry a mental health risk, particularly in culturally tactile societies. Further, increased psychological distress, particularly in more vulnerable groups prior to the pandemic, may lead to negative lifestyle changes e.g. lack of exercise, lack of sleep and increased alcohol consumption.
Stress and poor mental health have been linked to modulation of all aspects of the human microbiome. We are living in a microbial world; the brain has never existed without microbes (they may have even driven brain development!) and we know that microbes take part in maintaining our health (7).
Mental health and the skin microbiome
Emotions associated with stress, including depression and anxiety, have been implicated in skin conditions. By altering the gut microbiota and increasing intestinal permeability, stress can potentially contribute to skin disorders, such as inflammation – suggesting the existence of a gut-brain-skin axis.
Over the years an expanding body of research has shed light on the gut-skin axis in the context of acne severity, connected to gut microbes and diet (8). More recently, the link between skin barrier function and depression (brain) has been suggested (9). But this begs the question: how does the skin microbiome contribute?
The skin microbiome has been shown to impact the skin immune response, independent of the gut microbiome (10). ‘Homeostatic immunity’ means our skin exhibits an adaptive response to skin commensal bacteria without causing inflammation i.e. maintains a stable state.
A recently published study on stress-induced itching discusses the new microbiome-skin-brain axis. This axis is an interplay of the skin microbiome, skin barrier function, the skin immune system and the sensory nerves. The skin supports its microbiome, which in turn strengthens the skin barrier function, its immune system and helps the skin communicate with other organs, including the brain via the sensory nerves (11). There are multiple routes of communication including 1) microbial neurochemicals (such as acetylcholine and histamine), 2) nerve signals carried by sensory nerve fibres, and 3) messages of the immune system transferred by cytokines (10).
Microbes residing on the skin exist in the context of complex interactions. These are both microbe-microbe and human-microbe, likely with consequences for systemic immunity of the human body. The superficial skin microbiome – described as the “microbial fingerprint” – is unique to each individual. It is likely that the microflora living on the uncovered areas of our body will change (as a result of over-washing and sanitisation, the use of protective personal equipment and perhaps even the contribution of mental health) due to our isolation and change in habits, with an unprecedented and, on balance, more likely negative impact on skin health.