Granuloma annulare is caused by an overactive immune response in the skin, but the exact reason this response starts remains unknown. The condition produces ring-shaped, raised bumps on the skin that are usually painless and harmless. While no single cause has been pinpointed, researchers have identified the immune mechanism behind the lesions and several factors that can trigger them.
The Immune Reaction Behind the Lesions
Granuloma annulare appears to be driven by a type of delayed immune reaction in the skin. Specific immune cells called helper T cells accumulate at the site and release a signaling molecule (interferon-gamma) that activates macrophages, the immune system’s cleanup crew. Once activated, these macrophages release enzymes that break down connective tissue in the skin, specifically collagen. This tissue breakdown is what creates the characteristic bumps and rings visible on the surface.
There’s also evidence that the normal first responders to inflammation, neutrophils, don’t arrive at the site properly in people with granuloma annulare. When neutrophils fail to show up, macrophages take over the inflammatory process instead. This shift produces the granuloma pattern (clusters of immune cells walling off an area) rather than the typical swelling and redness you’d see with a normal inflammatory response. Under a microscope, lesions show a telltale triad: degraded collagen fibers, a dense infiltrate of immune cells, and deposits of a gel-like substance called mucin. That mucin deposit actually helps distinguish granuloma annulare from similar-looking skin conditions.
Known Triggers
Even though the root cause is unclear, a number of external events can set off the immune reaction. These include:
- Minor skin injuries or trauma to the area
- Insect or animal bites
- Infections, particularly hepatitis
- Vaccinations and tuberculin skin tests
- Sun exposure
- Certain medications
Not everyone with granuloma annulare can point to a specific trigger. Many cases appear without any obvious preceding event, which is part of what makes the condition frustrating to understand. When a trigger is identifiable, lesions typically develop at or near the site of the injury or exposure.
Medications That Can Cause It
Several drugs have been linked to granuloma annulare, including amlodipine (a blood pressure medication), allopurinol (used for gout), diclofenac (an anti-inflammatory pain reliever), quinidine (a heart rhythm drug), gold compounds (used in some arthritis treatments), and intranasal calcitonin. Drug-induced cases are relatively uncommon, but if lesions appear shortly after starting a new medication, that timing is worth noting for your doctor.
The Diabetes Connection
Diabetes is the health condition most commonly discussed alongside granuloma annulare, and the link is real but modest. A large population-based study of over 5,000 people with granuloma annulare found that 21% also had diabetes, compared to 13% of matched controls. That translates to roughly 67% higher odds of having diabetes if you have granuloma annulare. People with granuloma annulare were also slightly more likely to develop diabetes in the future.
That said, most people with granuloma annulare do not have diabetes. The association is strong enough to be worth screening for, especially if you have other risk factors for diabetes, but granuloma annulare on its own is not a reliable indicator of blood sugar problems.
Other Health Conditions Linked to It
Researchers have looked at whether granuloma annulare clusters with other systemic diseases, and the results are mixed. A case-control study of 224 patients found significantly higher rates of high cholesterol among those with granuloma annulare: 48% had elevated cholesterol compared to 35% of controls. However, the study authors themselves were skeptical about a meaningful biological connection and cautioned against reading too much into it.
Thyroid disease, particularly hypothyroidism, shows up slightly more often in granuloma annulare patients (15% versus about 10% in controls), but the difference has not reached statistical significance in studies. Hepatitis C has also appeared at higher rates in some studies. In rare cases, granuloma annulare can occur as a paraneoplastic phenomenon, meaning it develops in response to an underlying cancer. When this happens, lung cancer is the most frequently associated malignancy, though paraneoplastic granuloma annulare is uncommon.
Who Gets It Most Often
Granuloma annulare affects women about four times more often than men. While it can appear at any age, it’s most common in older adults. A cross-sectional study using U.S. health data found that the average age of people with granuloma annulare was 61, and 72% of cases occurred in people aged 55 or older. The highest prevalence was in the 65 to 74 age group. Children can develop it too, particularly the localized form on the hands and feet, but the widespread (generalized) form is more typical of older adults.
Why It Often Resolves on Its Own
Because granuloma annulare is driven by an immune reaction rather than an infection or structural problem, many cases resolve without treatment as the immune response naturally subsides. Localized lesions often clear within two years, though they can recur in the same spot or elsewhere. The generalized form, which covers larger areas of the body, tends to be more persistent and is more commonly associated with underlying conditions like diabetes or high cholesterol. If your lesions are spreading, lasting longer than expected, or appeared suddenly across multiple areas, that pattern is more likely to prompt further workup for associated conditions.