Introduction

Pregnancy-related dermatoses can include a variety of skin conditions that arise because of the complex immunological and hormonal changes during gestation. Two disorders which appear similar are Pruritic Urticarial Papules and Plaques of Pregnancy (PUPPP) and Pemphigoid Gestationis (PG); however, these differ in cause, severity, and clinical management. PUPPP is a common condition which doesn't affect the fetus, whereas PG is a rarer but more serious autoimmune disease which can lead to adverse pregnancy outcomes. It is very important to distinguish between the two, as the correct treatment approach and monitoring needs to be applied.¹

Basic definitions

PUPPP

Pruritic Urticarial Papules and Plaques of Pregnancy (PUPPP), also known as Polymorphic Eruption of Pregnancy, is a common Pregnancy-related dermatosis. This is a benign inflammatory skin condition which is often seen in first-time pregnancies and those with multiple gestation pregnancies. PUPPP typically arises in the third trimester of pregnancy. It is characterised by a sudden appearance of intense red and itchy papules and plaques around the stretch marks. The specific cause remains unidentified, but it is related to abdominal skin stretches or changes in hormones. PUPPP is not an autoimmune disorder and doesn't pose any risk to the fetus.

Pemphigoid gestationis (PG)

Pemphigoid Gestationis (PG), also known as herpes gestationis, is a very rare autoimmune blistering dermatosis of pregnancy which occurs in approximately 1 in 50,000 pregnancies.² Pemphigoid gestationis typically presents during the second or third trimester but can also appear during the postpartum period. PG symptoms for the newborn begin with itchy lesions around the umbilical cord area, which can evolve to fluid-filled blisters. 

This condition is due to the maternal autoantibodies (IgG, immunoglobulin G) targeting components of the skin (notably BP180, a protein maintaining skin integrity), leading to complement activation and blister formation. In contrast to PUPPP, PG is linked to possible fetal concerns such as preterm birth, fetal growth limitations, and temporary neonatal lesions brought on by passive antibody transmission. Systemic corticosteroid therapy is frequently necessary for PG, and relapses may occur with subsequent pregnancies, menstruation, or the use of hormonal contraceptives.³

Key differences between PUPPP and PG

Timing of onset

The timing of when the rash starts to develop can give us an initial clue to the underlying condition.

PUPPP most often occurs during the third trimester, around 35 weeks of gestation, and is very common in first-time pregnancies. It can also appear slightly early in twin or triplet pregnancies as the abdominal stretching starts to occur sooner. This condition will start to resolve rapidly after delivery.⁴

PG has a more variable onset as it ranges from the second trimester (can be as early as 13-14 weeks) to the postpartum period. Many cases are present in the third trimester; however, PG tends to have relapsing patterns whereby it can flare up again after delivery and other circumstances. ³

Associated risk factors

Knowing the predisposing factors can help with early detection and risk stratification:

PUPPP is generally thought to be triggered by connective tissue damage because of the rapid skin stretching, which can lead to an exposure of dermal antigens that trigger inflammatory responses. This occurs more frequently in:

• Primigravid people (pregnant for the first time)
• Multiple pregnancies (twins, triplets)
• The maternal parent is experiencing excessive or rapid weight gain
• Fetuses assigned male at birth (AMAB) have also been reported as a potential risk factor in some studies

PG is a type II hypersensitivity autoimmune condition in which maternal IgG autoantibodies target BP180, a protein found in the skin. This causes the complement system to be activated, which causes blistering and inflammation. Risk factors include:

• Presence of HLA-DR3 or DR4 haplotypes
• Personal or family history of autoimmune diseases (e.g., thyroid disorders, type 1 diabetes)
• Prior history of PG, as the condition often recurs in future pregnancies ⁵

Symptoms and skin findings

The key to distinguishing between the two is the distribution and morphology of skin lesions:

• PUPPP:

PUPPP consists of extremely itchy, erythematous papules and plaques that usually begin in the lower abdomen and first appear in the abdominal striae (stretch marks). These lesions are not blistering, but they may combine to form larger plaques. The fact that PUPPP usually spares the umbilicus is a distinguishing characteristic. The rash does not affect the face, palms, soles, or mucosa, although it may spread to the thighs, upper arms, and buttocks.⁶

• Lesions are polymorphic, meaning they can vary in shape and size
• Excoriation may be present due to intense pruritus

• PG:

One of the main characteristics that sets PG apart is the itchy, urticarial (hive-like) plaques that first appear around the umbilicus. These develop into bullae, which are tight blisters filled with fluid that can erode, rupture, or crust. The body, limbs, palms, soles, and, infrequently, mucosal areas like the mouth or genitalia can all be affected by PG lesions, which have a tendency to spread centrifugally. In contrast to PUPPP, PG lesions frequently worsen or remain after giving birth, and they may leave scars or post-inflammatory hyperpigmentation.³

Histology & immunofluorescence

When many clinical features overlap, it is important to look at biopsy and immunopathological studies for a proper diagnosis:

Histological results in PUPPP are not specific. Despite the absence of blister formation, a skin biopsy may reveal perivascular lymphocytic infiltrates, dermal oedema, and infrequently, eosinophils. Autoantibodies and immune complex deposition are not present, as indicated by the negative direct immunofluorescence (DIF) result.

Histology of PG shows a subepidermal blister with a higher dermal infiltration that is rich in eosinophils. A linear band of complement component C3 (and occasionally IgG) along the dermoepidermal junction is visible in DIF, which is diagnostic. This pattern is pathognomonic for PG and sets it apart from other blistering conditions such as dermatitis herpetiformis or bullous pemphigoid.⁷

Maternal and fetal outcomes

The maternal and fetal outcomes of PUPPP and PG differ significantly, which makes the importance of accurate diagnosis essential. Whilst PUPPP is a benign condition, it can be intensely uncomfortable and itchy for the mother. Despite this, the condition doesn't pose any risk to the fetus and has no systemic complications for the mother. It usually resolves soon after delivery and isn't common to occur again in future pregnancies. 

In contrast to this, PG is an autoimmune disorder with serious complications. PG can flare up again during postpartum and can occur with more severity in future pregnancies. The higher risk of complications for the mother can include secondary skin infections. In terms of the fetus, PG is linked to an increased risk of preterm birth and lower than average birth weight. Around 10–15% of newborns may develop mild, self-limiting skin lesions due to transplacental antibody transfer. Because of these risks, PG-affected pregnancies often require enhanced monitoring and multidisciplinary care.⁵

Treatment approaches

The treatment techniques for PUPPP and PG range greatly due to the nature and severity of the conditions. Since PUPPP is a non-autoimmune, benign rash, its main treatment is symptomatic. Topical corticosteroids, oral antihistamines, and emollients to reduce inflammation and irritation are all part of the first-line treatment. Although it is rarely required, a brief course of systemic corticosteroids may be given in more severe situations. Long-term treatment is typically not necessary because the problem goes away on its own after birth.⁸

On the other hand, because of its immunological origin and the possibility of problems for both the mother and the foetus, PG frequently requires a more aggressive and prolonged therapy strategy. The foundation of treatment is systemic corticosteroids, like oral prednisone, which are usually needed to regulate blister formation and lower inflammation. 

Strong topical corticosteroids may be adequate in milder situations, especially during pregnancy, when systemic medication should be used with caution. Immunosuppressive medications such as azathioprine may be necessary for severe or resistant instances, particularly if symptoms continue after giving birth. Pruritus can also be treated with antihistamines as an adjuvant. Throughout the pregnancy and postpartum phase, thorough obstetric monitoring and a multidisciplinary care plan comprising dermatology and maternal-fetal medicine specialists are crucial due to the potential of foetal growth restriction and preterm delivery in PG.⁹

Conclusion

Distinguishing between Pruritic Urticarial Papules and Plaques of Pregnancy (PUPPP) and Pemphigoid Gestationis (PG) is crucial due to their differing causes, clinical courses, and implications for both maternal and fetal health. While PUPPP is a common, benign condition that primarily affects first-time mothers in late pregnancy and resolves shortly after delivery without complications, PG is a rare autoimmune blistering disorder that may persist postpartum and carries risks such as preterm birth and low birth weight.

Careful attention to clinical features like including rash distribution, presence or absence of blisters, and involvement of the umbilical area, as well as histological and immunofluorescence findings, is key to accurate diagnosis. Timely recognition allows for appropriate management: supportive treatment for PUPPP and immunosuppressive therapy with close obstetric monitoring for PG. Understanding these distinctions ensures better outcomes for both mother and baby, and helps guide long-term care, especially in cases of PG where recurrence is likely in future pregnancies.