How Do Bullous Pemphigoid and Pemphigus Vulgaris Differ?

While bullous pemphigoid and pemphigus vulgaris sound almost identical, they are two distinct autoimmune blistering diseases with different symptoms, blister types, and underlying causes. The main difference is where the blisters form in the skin. Bullous pemphigoid causes deep, “tense” blisters that are firm and hard to pop ^[1]. In contrast, pemphigus vulgaris causes superficial, “flaccid” blisters that rupture very easily, often leaving painful, open sores called erosions ^[1].

Additionally, bullous pemphigoid is much more common, generally affects older adults, and is usually characterized by intense itching ^[2][3]. Pemphigus vulgaris is rarer, tends to be more painful than itchy, and frequently starts with sores inside the mouth ^[4][5].

Both conditions are rare autoimmune diseases—meaning the immune system mistakenly attacks healthy tissue—but they are not contagious, and you did not do anything to cause them.

Quick Comparison

(Note: These are common patterns, but individual symptoms can overlap. Do not use this list to self-diagnose.)

The Blisters: Tense vs. Flaccid

The most recognizable clinical difference between the two conditions is the structural integrity of the blisters. This happens because the immune system attacks different targets in the skin.

• Bullous Pemphigoid (Tense Blisters): The immune system attacks the “anchors” (hemidesmosomes) that attach the top layer of skin (epidermis) to the deep layer (dermis) ^[6]. Because the blister forms deep under the sturdy top layer of skin, it is thick-roofed, firm, and tense ^[7]. These blisters do not break easily ^[1].
• Pemphigus Vulgaris (Flaccid Blisters): The immune system attacks the “glue” (desmosomes) that holds the individual skin cells together within the top layer of skin ^[6][8]. Because the blister forms closer to the surface with a very thin roof, it is fragile and flaccid ^[7]. These blisters rupture so quickly that a patient might only notice open sores—known as erosions (raw areas where the blister roof has peeled off)—rather than fully formed blisters ^[8].

Symptoms and Location

Where the disease strikes and how it feels also differ significantly, though there are always exceptions:

• Primary Sensation: Bullous pemphigoid commonly causes severe, sometimes debilitating itching ^[9]. Often, the itching and red, hive-like rashes begin weeks or months before any blisters actually appear (this is known as the prebullous phase) ^[3]. Pemphigus vulgaris, on the other hand, is usually characterized by sharp pain and burning, particularly when eating or swallowing, rather than itching ^[4].
• Primary Locations: Bullous pemphigoid primarily affects the skin, especially on the arms, legs, and torso ^[10]. It only occasionally affects the mucous membranes (the moist linings of the body, such as the mouth, eyes, throat, and genitals) ^[11]. Conversely, pemphigus vulgaris very frequently begins with painful blisters and sores inside the mouth, and can occur alongside lesions on the skin and other mucous membranes ^[4][12].

Important: Do not rule out either disease just because you don’t have the “classic” symptoms. Some people with bullous pemphigoid never develop actual blisters, and people with pemphigus vulgaris can also have widespread skin involvement.

Who Gets It?

Both diseases are chronic autoimmune conditions that require careful medical management ^[13], but their demographics differ:

• Frequency: Bullous pemphigoid is the most common autoimmune blistering disease ^[2]. Pemphigus vulgaris is much rarer ^[5].
• Age Patterns: Bullous pemphigoid typically affects older adults, with the incidence rising sharply after age 70 ^[2][14]. While pemphigus vulgaris also affects adults, it can begin slightly earlier in life, commonly in middle-aged or older adults ^[14].

How Doctors Tell Them Apart

Because treatments require specific anti-inflammatory or immunosuppressive medications, a dermatologist will not rely solely on looking at the blisters. They will typically perform a skin biopsy, which often involves taking two distinct samples:

1. For Microscopy (Histology): A sample is taken from a fresh blister. Under a microscope, the doctor can clearly see if the blister is deep (subepidermal), which points to bullous pemphigoid, or shallow (intraepidermal), which points to pemphigus vulgaris ^[15][7].
2. For Direct Immunofluorescence (DIF): A second sample is taken from normal-appearing skin right next to the blister. This specialized test shows the exact pattern and location of deposited antibodies in the tissue (for example, a linear pattern along the basement membrane for bullous pemphigoid, versus a network pattern between skin cells for pemphigus) ^[16].

To further support the diagnosis, your doctor may order blood tests (such as an ELISA test). These check your blood for the specific antibodies driving the disease. Bullous pemphigoid is associated with BP180 and BP230 antibodies, while pemphigus vulgaris is associated with desmoglein 1 and desmoglein 3 antibodies ^[17]. These tests are combined with your clinical symptoms and biopsy results to guide your specific treatment plan.

When to Seek Urgent Care

Do not deliberately pop or peel your blisters unless a doctor has safely shown you how, as this increases the risk of infection and delays healing. Seek prompt medical attention if you experience:

• Signs of infection: Increasing redness, warmth, swelling, pus, foul odor, or a fever.
• Mucosal emergencies: Difficulty breathing, an inability to swallow or drink fluids, or any eye pain or changes in your vision.
• Rapid spreading: Sores or blisters that multiply very quickly across your body.