The Major Subtypes of ILD

At a Glance

Interstitial Lung Disease (ILD) is an umbrella term for over 200 conditions. Getting an accurate diagnosis of your specific subtype—such as IPF, autoimmune ILD, or hypersensitivity pneumonitis—is critical because it dictates whether you need immune-suppressing drugs or anti-scarring medications.

Interstitial Lung Disease (ILD) is an “umbrella term” for over 200 conditions. Because many of these look identical in the early stages, your medical team must categorize your condition into a specific subtype ^[1]. This classification is the most important step in your care because it dictates whether you need medications to calm your immune system or medications to slow down scarring ^[2]^[3].

The Four Major Subtypes

Most patients will fall into one of these four categories based on the cause and behavior of the disease:

Idiopathic Pulmonary Fibrosis (IPF): “Idiopathic” means the cause is unknown. IPF is a specific form of lung scarring that occurs mostly in older adults. It is characterized by a “UIP” (Usual Interstitial Pneumonia) pattern on CT scans ^[4]. It does not involve the immune system in a typical way, so it is treated primarily with antifibrotics ^[3]^[5].
Connective Tissue Disease-Associated ILD (CTD-ILD): This occurs when an autoimmune disease (like Rheumatoid Arthritis, Scleroderma, or Lupus) attacks the lungs ^[2]. Because the root cause is an overactive immune system, the first line of treatment is usually immunosuppressants ^[3]^[6].
Hypersensitivity Pneumonitis (HP): This is caused by an allergic-like reaction to inhaled substances, such as bird feathers/droppings, mold, or certain farm dusts ^[7]. Identifying and removing the “trigger” is the most critical part of treatment.
Sarcoidosis: This condition involves the growth of tiny clumps of inflammatory cells (granulomas) in the lungs ^[8]. While it can cause scarring, it often responds very well to steroids or other immune-calming drugs ^[7].

“Progressive Fibrosing ILD” (PF-ILD): A Behavior, Not a Name

In recent years, doctors have identified a specific behavior called Progressive Pulmonary Fibrosis (PPF)—also known as Progressive Fibrosing ILD (PF-ILD) ^[9].

This is not a separate disease. Instead, it is a “behavior trait” that can happen to any subtype ^[7]. If a patient with CTD-ILD or HP continues to develop more lung scarring despite standard treatment, they are said to have a “progressive phenotype” ^[10]^[11].

Why this matters: If your disease behaves this way, your doctor may add antifibrotic medications to your regimen, even if your primary diagnosis is not IPF ^[12]^[13].

Why Accurate Subtyping is Critical

Getting the subtype right is essential because the wrong treatment can be ineffective or even harmful.

Feature	IPF	Autoimmune (CTD-ILD)	HP (Environmental)
Primary Driver	Pure Scarring (Fibrosis)	Immune System Attack	Environmental Trigger
Main Treatment	Antifibrotics ^[5]	Immunosuppressants ^[3]	Removal of trigger ^[7]
Role of Steroids	Usually avoided ^[14]	Often used first ^[6]	Often used to calm “flare”

If a patient with IPF is incorrectly treated with heavy immunosuppressants (like a patient with Lupus would be), it can actually worsen their condition ^[14]. Conversely, if a patient with autoimmune ILD only receives antifibrotics, the underlying immune attack on their lungs may continue unchecked ^[3]^[15]. This is why your team uses blood tests, imaging, and sometimes biopsies to be as precise as possible ^[16]^[17].

Common questions in this guide

What are the main subtypes of Interstitial Lung Disease (ILD)?

The four most common categories are Idiopathic Pulmonary Fibrosis (IPF), Connective Tissue Disease-Associated ILD (CTD-ILD), Hypersensitivity Pneumonitis (HP), and Sarcoidosis.

Why is it so important to know my specific ILD subtype?

Your specific subtype dictates your treatment plan. Some forms of ILD require medications to calm the immune system, while others need drugs to slow down lung scarring. Receiving the wrong treatment for your specific subtype can be ineffective or even harmful.

What does Progressive Fibrosing ILD (PF-ILD) mean?

Progressive Fibrosing ILD (PF-ILD) is not a separate disease, but rather a behavior trait where lung scarring continues to worsen despite standard treatment. If your condition behaves this way, your doctor may add anti-scarring medications to your regimen.

Can my environment cause Interstitial Lung Disease?

Yes, a specific subtype called Hypersensitivity Pneumonitis is caused by an allergic-like reaction to inhaled substances such as mold, bird droppings, or farm dust. Identifying and removing these environmental triggers is the most important part of treating this subtype.

How do doctors figure out which type of ILD I have?

Your medical team will use specialized CT scans to look for specific scarring patterns, run blood tests to rule out underlying autoimmune conditions, and review your history of environmental exposures and symptoms like joint stiffness or skin rashes.

Guide Contents

The Major Subtypes of ILD

The Four Major Subtypes

“Progressive Fibrosing ILD” (PF-ILD): A Behavior, Not a Name

Why Accurate Subtyping is Critical

Common questions in this guide

Appointments are short. Make every minute count.

Related questions

Get notified when new evidence is published on Interstitial lung disease.

Guide Contents

The Four Major Subtypes

“Progressive Fibrosing ILD” (PF-ILD): A Behavior, Not a Name

Why Accurate Subtyping is Critical

Common questions in this guide

Appointments are short. Make every minute count.

Related questions

Get notified when new evidence is published on Interstitial lung disease.

References