How Does Panniculitis Start? Understanding Its Complex Origins

October 2, 2025 •

4 min read

Panniculitis is an umbrella term for a group of conditions that cause inflammation of the subcutaneous fat layer. Understanding how does panniculitis start is crucial for proper diagnosis and treatment, as its onset can be triggered by a wide and sometimes surprising array of underlying factors.

Quick Summary

The onset of panniculitis varies widely, resulting from an inflammatory response in the fatty tissue under the skin that can be triggered by infections, physical trauma, medications, autoimmune disorders, and underlying systemic diseases.

Key Points

Infections are a major trigger: Bacterial and viral infections, both localized and systemic, are common starting points for panniculitis.
Physical trauma can initiate it: Direct injury, injections, or exposure to extreme cold can cause the inflammation to begin in the fatty layer.
Systemic diseases play a role: Autoimmune conditions like lupus, Crohn's disease, and pancreatitis are frequent underlying causes.
Medications and deficiencies: Certain drugs and genetic disorders like Alpha-1 Antitrypsin Deficiency can also be responsible for the onset.
Classification by inflammation site: Panniculitis is classified as septal or lobular based on where the inflammation begins in the fat layer, which guides diagnosis.
Onset can be sudden or gradual: While some forms start abruptly, others develop slowly alongside chronic underlying diseases.

A Multi-Faceted Onset: The Triggers Behind Panniculitis

Unlike many conditions with a single, clear cause, panniculitis is the result of an inflammatory process that can be set in motion by a multitude of factors. For some, the development is sudden, while for others, it is a gradual process tied to a chronic underlying condition. The resulting symptoms—painful, tender nodules beneath the skin—are a universal feature, but the path to their appearance is unique to the specific cause.

Infections: A Common Starting Point

One of the most frequent causes of panniculitis is an infection. This can be either a direct skin infection or a systemic infection elsewhere in the body that triggers an inflammatory reaction in the subcutaneous fat. Infectious triggers include:

Bacterial infections: Including common culprits like Streptococcus or Staphylococcus species, which can lead to abscess formation and inflammation.
Viral infections: Viruses such as HIV and others can trigger panniculitis in some individuals.
Fungal infections: Although less common, certain fungal infections can also lead to inflammation of the fat layer.
Mycobacterial infections: Including tuberculosis, which is notably associated with Erythema Induratum.

Physical Factors: Injury and Environment

Physical trauma and environmental conditions are another key category of triggers. The body's immune response to a localized injury or exposure can be a direct cause of panniculitis.

Trauma: A direct blow or injury to the skin can induce inflammation. Even a simple injection can sometimes lead to localized traumatic panniculitis.
Cold Exposure: Known as cold panniculitis, this form occurs after skin is exposed to extreme cold. It is most commonly seen in children who have been exposed to cold weather or even from sucking on a popsicle for a long time. It can also affect adults, such as skiers with inadequate clothing.

Underlying Systemic Diseases and Autoimmune Conditions

For many, panniculitis is a manifestation of a more complex systemic issue where the immune system misfires and attacks healthy tissue. The inflammatory cascade that begins these conditions is the same one that ultimately affects the subcutaneous fat.

Autoimmune diseases: Conditions such as systemic lupus erythematosus (lupus panniculitis), rheumatoid arthritis, and Crohn's disease can be significant drivers.
Pancreatic disorders: In rare cases, pancreatic disease, like pancreatitis or pancreatic cancer, can release enzymes that digest subcutaneous fat, causing pancreatic panniculitis.
Alpha-1 Antitrypsin Deficiency: A genetic disorder that can cause severe, recurrent panniculitis, often with ulceration.
Sarcoidosis: This inflammatory disease can cause panniculitis, where granulomas form in the fatty tissue.

Medications and Other Factors

Certain medications and other idiosyncratic reactions can also trigger the onset of panniculitis.

Medications: Some drugs, such as certain antibiotics (e.g., sulfonamides) and oral contraceptives, have been linked to drug-induced panniculitis.
Corticosteroid Withdrawal: Rapid withdrawal of systemic corticosteroids can sometimes trigger a type of panniculitis.
Idiopathic: In some cases, a cause is never identified, and the condition is labeled as idiopathic panniculitis.

A Histological View: Septal vs. Lobular Onset

To further understand how panniculitis starts, pathologists classify it based on the location of the inflammation within the fat layer. This distinction is crucial for diagnosis and can provide clues about the underlying cause. A deep skin biopsy is often required to make this determination.

Septal Panniculitis: Inflammation primarily affects the connective tissue (septa) that separates the fat lobules. Erythema nodosum is a common example of this type.
Lobular Panniculitis: Inflammation is centered within the fat lobules themselves. Cold panniculitis and pancreatic panniculitis are examples.
Mixed Panniculitis: Some types involve both the septa and the fat lobules, making a definitive classification more complex.

Comparison of Common Panniculitis Types


Feature	Erythema Nodosum	Cold Panniculitis	Pancreatic Panniculitis
Primary Cause	Infections (e.g., strep), medications, autoimmune issues, idiopathic	Exposure to extreme cold, trauma	Pancreatic disease (e.g., pancreatitis, cancer)
Inflammation Site	Septal, often without vasculitis	Lobular	Lobular, with extensive fat necrosis
Typical Location	Shins, lower legs	Cheeks, arms, legs (exposed areas)	Lower extremities, abdomen, trunk
Key Symptoms	Tender, red bumps; fever; joint pain	Firm, red-blue, cold-feeling nodules	Painful, purplish nodules; oily discharge; systemic symptoms
Who is Affected?	Primarily young women, though can affect all ages	Infants and young children are most common	Adults with pancreatic disorders

Conclusion: The Complex Tapestry of Panniculitis Onset

Pinpointing the exact beginning of panniculitis can be a diagnostic challenge due to the wide range of potential triggers. From a simple bacterial infection to a complex autoimmune disorder, the pathway to inflammation of the subcutaneous fat is diverse. This complexity underscores the importance of a thorough medical evaluation, including a review of medical history, potential exposures, and a physical examination. While the visible signs may be similar across different types, understanding the underlying mechanism is the key to providing effective, targeted treatment and addressing the root cause of the problem.

Frequently Asked Questions

Infections are considered one of the most common causes, with specific examples including bacterial infections from Streptococcus and viral illnesses. However, the exact cause is often unknown and can be highly variable depending on the specific type of panniculitis.

Yes, a form of the condition called traumatic panniculitis can begin after an injury or trauma to the skin. This occurs when the body's inflammatory response to the trauma affects the subcutaneous fat.

Not always. While many cases are triggered by an underlying systemic disease, autoimmune condition, or infection, some instances are idiopathic, meaning they arise spontaneously without any clear identifiable cause.

Yes, cold panniculitis, also known as popsicle panniculitis in children, can begin after prolonged exposure to cold temperatures. This often affects exposed areas of the body, such as the face or limbs.

Yes, certain medications, including sulfonamide antibiotics, birth control pills, and large doses of corticosteroids, have been known to cause panniculitis as an adverse reaction.

Panniculitis typically starts with the formation of tender, deep nodules or bumps under the skin. The skin over these bumps may then become discolored, appearing red, brown, or purple.

Doctors will conduct a thorough medical history and physical examination. In many cases, a deep skin biopsy is performed to determine if the inflammation is septal or lobular, which helps narrow down the potential triggers and guide treatment.