90% of Serotonin Is Produced in the Gut: How the Gut–Brain Axis Works and the Role of Aromatherapy

We’re used to thinking that mood is formed in the brain, and that serotonin is purely about neurons and psychology. But in reality, about 90% of serotonin is produced in the gut—not in the brain. This fundamentally changes how we understand the gut’s influence on mood, stress levels, and overall well-being.

The gut is a complex biological system. It is home to trillions of microorganisms that form the gut microbiome, which plays an active role in serotonin synthesis.

Most serotonin is produced from the amino acid tryptophan, and this process largely depends on the microbiota. In other words, the gut microbiome directly affects how much serotonin is available to the body. Microorganisms essentially become participants in processes that shape our emotional state.

The connection between the gut and the brain is so strong that it has been defined as a separate system—the gut–brain axis. This is a bidirectional communication channel that operates through the nervous system (especially the vagus nerve), hormones, and immune signaling.

The gut sends information about its condition to the brain, while the brain influences gut function. That’s why stress can cause digestive issues, and gut imbalances can affect mood, anxiety, and even cognitive function. The gut–brain axis is key to understanding how physiology influences emotions.

The gut microbiome regulates several processes that impact well-being. It supports the integrity of the gut barrier, participates in nutrient metabolism, and influences the immune system.

When the microbiome is diverse and balanced, the gut–brain axis functions steadily. When this balance is disrupted (a condition known as dysbiosis), inflammation increases, metabolism changes, and neurotransmitter regulation—particularly serotonin—is impaired. As a result, this may manifest not only as digestive problems but also as mood changes, increased anxiety, or fatigue.

Modern lifestyle significantly affects the gut microbiome. The most impactful factors include chronic stress, frequent antibiotic use, low-fiber diets, processed foods, lack of sleep, and excessive environmental sterility. All of these gradually reduce microbial diversity—and with it, the stability of processes underlying the gut–brain axis and serotonin production.

At first glance, aromatherapy and the gut microbiome may seem like completely different worlds. However, research suggests that essential oils can influence the microbial environment more subtly than it might seem.

Despite their antimicrobial properties, some essential oils act selectively: they can inhibit potentially pathogenic microorganisms without disrupting the balance of beneficial microflora—or even support it.

For example, compounds such as thymol and carvacrol, found in oregano and thyme, are associated with reducing harmful bacteria while supporting beneficial ones. Other essential oils, including lavender and sweet orange, are linked to reduced inflammation and support of the intestinal barrier function.

In aromatherapy, this effect is sometimes described as eubiotic action. This refers not to the complete elimination of microorganisms, but to the ability to influence the gut microbiome more selectively. Unlike antibiotics, which often act broadly and reduce overall microbial diversity, some essential oils may suppress pathogens without disrupting—or even while supporting—commensal bacterial populations.

This approach is particularly important in the context of the gut–brain axis, as a diverse and balanced microbiome is associated with stable neurotransmitter synthesis, including serotonin. Maintaining this balance helps reduce inflammation, support the integrity of the gut barrier, and positively influence mood and overall well-being. This is fundamentally different from the non-selective action of many antibiotics.

Peppermint essential oil deserves special attention. It is well studied in the context of irritable bowel syndrome and is often used to support digestion. Its effects are associated with reducing spasms, improving gut motility, and lowering inflammation. In turn, this may positively affect not only digestion but also overall well-being.

Aromatherapy also works through the nervous system. The inhalation pathway (via smell) directly affects the brain’s limbic system, which regulates emotions and stress. Reducing stress is an important factor in supporting the microbiome and the proper functioning of the gut–brain axis.

It’s also important not to overlook hydrosols in this context. They contain water-soluble bioactive compounds of plants, as well as hydrophilic molecules of essential oils, but in much lower concentrations. This allows them to act gently and be used regularly.

They don’t have a harsh effect, but they can become part of daily rituals that support hydration, promote digestive comfort, and help reduce stress levels. Hydrosols such as yarrow and peppermint have a strong affinity with the gastrointestinal tract, offer detoxifying effects, support metabolism, provide digestive benefits, and help maintain healthy gut flora. Moreover, hydrosols are generally easier for the body to digest and metabolize compared to essential oils.

Aromatherapy works best when it becomes part of regular rituals. Below are simple formulas that support digestion, the gut microbiome, and help reduce stress.

Abdominal Massage Blend

• 15 ml jojoba carrier oil
• 3 drops peppermint essential oil
• 3 drops lavender essential oil
• 2 drops sweet orange essential oil

Apply to the abdominal area using gentle clockwise circular motions 1–2 times a day or as needed. This blend helps reduce spasms, support gut motility, and relieve post-meal discomfort.

Digestive Tea Booster

• 1 drop ginger essential oil
• 1 spray peppermint hydrosol
• 1 tbsp honey
• 150 ml hot herbal tea (about 70–80°C, not boiling)

1. Mix the essential oil with honey using a toothpick
2. Add the mixture to the tea and stir thoroughly
3. Spray in peppermint hydrosol and stir again
4. Drink slowly in small sips after meals

Morning Detox

• 200 ml warm water
• 1–2 sprays yarrow hydrosol
• 1–2 sprays peppermint hydrosol

1. Stir well
2. Drink in the morning on an empty stomach to gently awaken and activate digestion

Evening Anti-Stress Tea

• 150 ml warm (not boiling) water
• 2 tsp German chamomile hydrosol
• ½ tsp honey (optional)

Helps calm the nervous system before sleep.

For the gut–brain axis to function harmoniously, it needs support. Aromatherapy can become a gentle yet effective tool that supports gut health and forms the foundation of stable physical and emotional well-being.

To support gut function, it’s enough to choose high-quality, food-grade essential oils from Aroma Fields. You can also find hydrosols on our website that will complement your routine.