The Black Death moved across Europe from 1347 to 1353 CE, with mortality rates reaching as high as 60% in some areas. Although its impact is well documented, the precise reasons for when and how the pandemic began remain unclear.

Climate Records Reveal Signs of a Major Eruption

To explore these questions, Martin Bauch and Ulf Büntgen evaluated earlier research on tree ring growth from eight regions in Europe, measurements of volcanic sulfur preserved in Antarctic and Greenland ice cores, and written reports from the fourteenth century. Together, these records point to a significant volcanic eruption somewhere in the tropics around 1345 CE. The eruption appears to have increased atmospheric sulfur and ash, which contributed to colder and wetter conditions across southern Europe and the Mediterranean.

Historical accounts describe widespread crop failures and famine during this period in Spain, southern France, northern and central Italy, Egypt, and the Levant. These hardships prompted Italian maritime powers -- such as Venice and Genoa -- to negotiate a ceasefire in a conflict with the Mongols of the Golden Horde so they could secure grain shipments from the Black Sea region around 1347 CE.

Grain Imports and the Possible Spread of Plague

Venetian sources state that these imports helped prevent mass starvation. However, the timing of arriving grain ships and the first plague outbreaks in cities that received them raises another possibility. Fleas carrying Yersinia pestis may have traveled with the grain. As the shipments were moved to additional cities, including Padua, these fleas could have helped accelerate the spread of the Black Death throughout Europe.

The authors conclude that this combination of climatic disruption, famine, and grain transport offers a plausible explanation for how the Black Death began and spread across Europe.

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The study, published in the Journal of Herbal Medicine, reports that garlic-based mouthwash may produce more discomfort than chlorhexidine but appears to provide longer-lasting residual activity.

"Chlorhexidine is widely used as a gold standard mouthwash but is associated with side effects and concerns over antimicrobial resistance," the authors explain. "Garlic (Allium sativum), known for natural antimicrobial properties, has emerged as a potential alternative."

Systematic Review Compares Garlic and Chlorhexidine

The researchers based their conclusions on a systematic review examining how garlic extract performs against chlorhexidine in clinical settings and whether it can realistically function as an herbal substitute.

Their analysis followed the Preferred Reporting Items for Systematic Reviews and Meta-analyses 2020 guidelines, which are designed to increase the reliability and transparency of systematic reviews and meta-analyses. The authors also used the PICO framework to structure their clinical research questions.

"A total of 389 articles were identified from six electronic databases in January 2024, and an additional 13 articles were included through manual citation searching. After removing duplicates and applying inclusion and exclusion criteria, only five articles were included," they report.

Review Finds Comparable Antimicrobial Performance

The selected literature consisted of randomized controlled trials and clinical studies with varying designs and low-to-moderate risks of bias. Overall, the authors found that higher concentrations of garlic extract mouthwash showed antimicrobial results similar to those of chlorhexidine.

"The effectiveness varied based on mouthwash concentration and duration of application, contributing to differences in outcomes," the review noted. "Some studies favored chlorhexidine for maintaining higher plaque/salivary pH, while others reported garlic extract to be more effective at certain concentrations. However, garlic mouthwash may cause greater discomfort."

Side Effects and Patient Considerations

Although garlic extract can produce side effects, they are typically milder than those associated with synthetic chemicals. Reported issues include a burning sensation and unpleasant odor, which may influence whether patients are willing to switch from chlorhexidine to garlic-based options.

Even with these drawbacks, the review offers strong support for the clinical antimicrobial activity of garlic extract, reporting "significant reductions in bacterial counts from baseline … suggesting the possible use of garlic extract mouthwash as a viable alternative to chlorhexidine in certain contexts."

The authors recommend additional clinical trials with larger participant numbers and longer follow-up periods to confirm the "effectiveness and improve clinical applicability" of garlic as an alternative to chlorhexidine, which is still considered the gold standard antimicrobial mouthwash.

Garlic's Long History as a Natural Antimicrobial

Garlic has long been recognized as one of the most potent naturally occurring antibacterial and antifungal crops. Scientific interest has focused particularly on allicin, a compound known for its strong antimicrobial activity. Although classified botanically as a vegetable, garlic is commonly used as both an herb and a spice.

Worldwide garlic usage reached about 30 million metric tons in 2024. China accounted for nearly 80 percent of global consumption and production. That same year, the global garlic extract market was valued at more than 15 billion dollars.

Growing Interest in Herbal Oral Care Alternatives

Garlic extracts are widely available in various health products over-the-counter. By comparison, synthetic agents like chlorhexidine usually require a prescription from a dentist or physician.

"Antimicrobial mouthwashes constitute an essential adjunct element in oral and dental care, acting against oral diseases caused by bacteria, fungi, or viruses attacking oral hard or soft tissues," the review states. "Different antimicrobial mouthwashes, whether available over-the-counter or on prescription, can be used in the management of gingivitis, dental caries, periodontal diseases, halitosis, etc."

Evidence Expands but Clinical Gaps Remain

The review points to numerous studies that demonstrate antimicrobial effects of garlic extracts against a wide range of bacteria, fungi, and viruses. It also notes that garlic extract has been explored in areas such as denture stomatitis, dentinal tubule disinfection, and intracanal medication.

"These studies have contributed to understanding the antimicrobial role of garlic extract in comparison to synthetic agents like chlorhexidine," the authors write. "However, most studies are in vitro, vary in methods, and lack clinical standardization, highlighting the need for further research to confirm garlic's efficacy in dental practice. This uncertainty presents a significant gap in the literature on evidence-based antimicrobial therapies."

For hundreds of thousands of years, humans evolved to meet the physical and psychological demands of hunter-gatherer life, which required frequent movement, short bursts of intense stress and daily exposure to natural settings. Industrialization has altered these conditions within only a few centuries by adding noise, air and light pollution, microplastics, pesticides, continuous sensory input, artificial lighting, processed foods and long periods of sitting.

"In our ancestral environments, we were well adapted to deal with acute stress to evade or confront predators," says Colin Shaw, who leads the Human Evolutionary EcoPhysiology (HEEP) research group with Daniel Longman. "The lion would come around occasionally, and you had to be ready to defend yourself -- or run. The key is that the lion goes away again."

Modern stressors such as traffic, workplace pressure, social media and persistent noise activate the same biological pathways that once helped humans survive predators. Unlike the rapid resolution our ancestors experienced, these stressors rarely subside. "Our body reacts as though all these stressors were lions," Longman explains. "Whether it's a difficult discussion with your boss or traffic noise, your stress response system is still the same as if you were facing lion after lion. As a result, you have a very powerful response from your nervous system, but no recovery."

Industrialization and Its Impact on Health and Reproduction

In their review, Shaw and Longman evaluate research suggesting that the shift toward industrial and urban living is reducing human evolutionary fitness. Evolutionary success depends on both survival and reproduction, and the authors argue that both have been negatively influenced since industrialization began.

They highlight falling fertility rates across much of the world and increasing rates of inflammatory and autoimmune conditions as evidence that modern environments are placing stress on human biology. "There's a paradox where, on the one hand, we've created tremendous wealth, comfort and healthcare for a lot of people on the planet," Shaw says, "but on the other hand, some of these industrial achievements are having detrimental effects on our immune, cognitive, physical and reproductive functions."

One of the most studied examples is the steady decline in sperm count and sperm motility observed since the 1950s. Shaw notes that these trends appear to be linked to environmental exposures. "This is believed to be tied to pesticides and herbicides in food, but also to microplastics," he says.

Searching for Solutions That Support Human Wellbeing

Technological and environmental conditions continue to change far more rapidly than biological evolution can respond to. "Biological adaptation is very slow. Longer-term genetic adaptations are multigenerational -- tens to hundreds of thousands of years," Shaw says.

According to the researchers, this means the mismatch between human physiology and modern living conditions will not correct itself through natural evolutionary processes. Instead, they argue that societies must take active steps to reduce these pressures by strengthening connections to nature and creating healthier, more sustainable environments.

Addressing this mismatch requires both cultural and environmental changes. Shaw suggests treating nature as a crucial component of public health and protecting or restoring landscapes that resemble those in which humans originally evolved. He also advocates for rethinking city design to better align with human physiology and reduce harmful exposures.

"Our research can identify which stimuli most affect blood pressure, heart rate or immune function, for example, and pass that knowledge on to decision-makers," Shaw says. "We need to get our cities right -- and at the same time regenerate, value and spend more time in natural spaces."