Inflammation is your immune system’s response to anything it perceives as a threat, from a cut on your finger to bacteria in your lungs. In the short term, this response is protective. But when it stays switched on for weeks, months, or years, it becomes a driver of chronic disease. The causes range from what you eat and how you sleep to the fat stored around your organs and the air you breathe.
How the Inflammatory Response Works
When your body detects an invader or injury, immune cells release signaling proteins called cytokines. Two of the most important are TNF-alpha and IL-1 beta. TNF-alpha is produced by immune cells called macrophages, but only after they detect an inflammatory trigger. IL-1 beta starts as an inactive precursor inside the cell, gets activated by an enzyme, and is then pushed directly out into surrounding tissue. These molecules recruit more immune cells to the site, increase blood flow, and create the redness, swelling, and heat you associate with inflammation.
This system is designed to turn on fast and turn off once the threat is handled. Problems start when the signals never stop. Chronic low-grade inflammation produces a persistent, subtle elevation in these same cytokines, typically two to three times above normal baseline levels. Over time, that low hum of inflammation contributes to heart disease, type 2 diabetes, fatty liver disease, and many other conditions.
How Body Fat Fuels Inflammation
Fat tissue is not just energy storage. It functions as an endocrine organ, actively releasing hormones and inflammatory signals into your bloodstream. The type that matters most is visceral fat, the deep fat packed between your organs around the intestines and kidneys. Unlike the fat just under your skin, visceral fat is densely populated with immune cells that shift toward an inflammatory profile as fat stores grow.
During obesity, immune cells accumulate inside visceral fat tissue, altering the local environment and impairing your body’s ability to respond to insulin. This creates a feedback loop: inflammation worsens insulin resistance, insulin resistance promotes more fat storage, and more fat means more inflammation. Saturated fats in the diet add to this directly by triggering inflammation in fat tissue itself.
Foods That Trigger Inflammation
Several common dietary ingredients push the immune system toward a pro-inflammatory state. Processed sugars are among the most potent, directly stimulating cytokine release. Trans fats, found in foods containing partially hydrogenated oils, trigger systemic inflammation throughout the body. Refined carbohydrates like white bread and pastries are high-glycemic foods that fuel the production of compounds called advanced glycation end products, which stimulate inflammatory pathways.
The balance between two types of dietary fat also matters. Omega-6 fatty acids, found in corn oil, soybean oil, and many processed foods, are not harmful in small amounts. But in excess, they prompt your body to produce pro-inflammatory chemicals. Most Western diets are heavily skewed toward omega-6 and low in omega-3 fatty acids, which have the opposite, anti-inflammatory effect. For people with celiac disease, gluten sets off an autoimmune response that damages the small intestine and can cause joint pain, though this is specific to those with a genetic predisposition rather than a universal trigger.
What Happens When Your Gut Barrier Weakens
Your intestinal lining acts as a selective barrier, letting nutrients through while keeping bacteria and their byproducts out. When that barrier breaks down, a condition sometimes called “leaky gut,” bacterial fragments called lipopolysaccharides (LPS) slip through into the bloodstream. LPS is a component of the outer coating of certain gut bacteria, and it is one of the most powerful inflammatory triggers known. Even small amounts in the blood activate immune receptors in the liver and other organs, setting off a sustained inflammatory response.
This process has been directly linked to fatty liver disease in both its alcohol-related and non-alcohol-related forms. Gut dysbiosis, an imbalance in the types of bacteria living in your intestines, makes barrier breakdown more likely. Diets high in processed food and low in fiber tend to shift the gut microbiome in ways that weaken the barrier and increase LPS leakage.
Physical Inactivity and the Missing Anti-Inflammatory Signal
When your muscles contract during exercise, they release their own set of signaling molecules called myokines. After a bout of aerobic exercise, your body produces a cascade of anti-inflammatory compounds that actively counterbalance the inflammatory signals circulating in your blood. This is one of the primary mechanisms behind the well-documented health benefits of regular physical activity.
When you’re sedentary, that anti-inflammatory signal simply doesn’t get produced. Cross-sectional studies consistently show that physically inactive people have mildly elevated levels of multiple inflammatory markers, including CRP and TNF-alpha, at two to three times above what’s seen in active individuals. Over years, this contributes to the association between sedentary behavior and chronic diseases like heart disease, type 2 diabetes, and certain cancers. The relationship works in both directions: exercise suppresses inflammation, and inactivity permits it to build.
Sleep Loss and Stress
Consistently short sleep is linked to higher levels of C-reactive protein (CRP), one of the most commonly measured markers of systemic inflammation. A large meta-analysis published in Biological Psychiatry found that shorter sleep duration was associated with elevated CRP, though the relationship with other inflammatory markers like IL-6 was less clear. The effect appears to be driven more by habitual short sleep than by a single bad night, suggesting that your long-term sleep patterns matter more than the occasional late evening.
Chronic psychological stress operates through a related pathway. Stress hormones like cortisol are anti-inflammatory in short bursts, but under chronic stress, your immune cells become less sensitive to cortisol’s dampening effect. The result is that inflammatory processes run less checked, contributing to the same low-grade inflammation seen with poor sleep and inactivity.
Air Pollution and Environmental Toxins
Fine particulate matter, particles smaller than 2.5 micrometers (PM2.5), is small enough to pass deep into the lungs and trigger an inflammatory response in both the respiratory and circulatory systems. Once inhaled and deposited in lung tissue, these particles provoke the release of inflammatory mediators like nitric oxide and interleukins. Some chemical components, particularly smaller aromatic compounds, can cross directly from the lungs into the bloodstream, where they interfere with hormonal regulation and activate inflammatory pathways in distant organs.
This means that people living near highways, industrial areas, or in cities with poor air quality carry a baseline inflammatory burden that has nothing to do with their diet or exercise habits. Long-term PM2.5 exposure is associated with higher rates of cardiovascular disease, and inflammation is the primary mechanism connecting the two.
Aging and Cellular Wear
As you age, damaged cells accumulate throughout your tissues. Rather than dying off cleanly, many of these cells enter a state called senescence: they stop dividing but remain metabolically active, pumping out a cocktail of inflammatory cytokines, growth factors, and tissue-degrading enzymes. This output, known as the senescence-associated secretory phenotype (SASP), includes IL-6, TNF-alpha, and IL-1 beta, the same core inflammatory molecules your immune system uses to fight infections.
The steady buildup of these senescent cells over decades creates what researchers call “inflammaging,” a chronic, low-grade inflammatory state that is now recognized as a central feature of biological aging. SASP components also break down the structural scaffolding between cells and promote scarring in organs like the liver, kidneys, and lungs. This helps explain why inflammatory diseases become far more common with age, even in people who maintain healthy lifestyles.
How Inflammation Is Measured
The most widely used blood test for systemic inflammation is the high-sensitivity C-reactive protein test (hs-CRP). Your liver produces CRP in response to inflammatory signals, so its level in the blood reflects how much inflammation is active throughout your body. According to Mayo Clinic guidelines, an hs-CRP below 2.0 mg/L is associated with lower cardiovascular risk, while 2.0 mg/L or above signals higher risk, including a greater chance of heart attack.
A single elevated reading doesn’t necessarily mean you have a chronic problem, since infections, injuries, and even intense exercise can temporarily spike CRP. Doctors typically look at the result alongside other risk factors. If your hs-CRP is persistently elevated, it points toward one or more of the underlying drivers covered here: excess body fat, poor diet, inactivity, sleep disruption, or environmental exposures. Identifying and addressing those root causes is the most effective way to bring inflammation back to healthy levels.