Diagnosing blistering skin conditions

This article identifies a number of different blistering conditions and provides an overview of their management.

Eczema herpeticum: small, very even, punched-out blisters
Eczema herpeticum: small, very even, punched-out blisters

A blister describes any raised, fluid-filled skin lesion. Small blisters under 0.5cm are called vesicles, while larger blisters are known as bullae.

Friction blisters

Friction blisters are very common and occur on the soles, palms and heels, where the stratum corneum is thicker (friction on thinner skin causes erosions). Poorly fitting shoes are a frequent cause, while on the palms they occur from gripping tools or sports equipment.

Usually there is no problem with this diagnosis. Such blisters are best managed by draining the fluid from bigger ones with a sterile needle, but leaving the blister roof intact to serve as a dressing. This relieves the discomfort and protects the site from infection.

Gel plasters can protect smaller blisters and prevent new ones. If the blister roof is already fully or partially removed, it needs to be treated as a wound, with dressings and possibly an antiseptic or antibiotic cream.

Most friction blisters heal without problem, but they can sometimes lead to cellulitis and septicaemia, especially in patients with diabetes, the elderly or the immunosuppressed.

Insect bites

Insect bites frequently blister, probably as a result of being scratched. Such blisters are often formed on the lower legs and should be treated in the same way as friction blisters, along with oral antihistamines and topical steroids to stop irritation. Insect bites are often grouped or linear.


Unlike scabies in an adult, scabies in a small child or infant can present with small blisters on the base of the feet and the palms. This is often mistaken for eczema.

Both conditions can coexist and when this occurs, making a correct diagnosis can be a challenge. Using a dermatoscope greatly assists this process, because the head parts of the scabies mite can be seen as a dark triangle under the skin and the burrows of the mite become much more obvious.1

Treatment for scabies should involve not only the infant, but all members of the household (older children and adults). A topical scabicide should be used over the entire skin surface of the infant, and from the neck down for the others. Ideally, everyone should be treated on the same day and the process repeated a week later.

Infective causes of blistering

Herpes simplex and herpes zoster

Herpes simplex and herpes zoster cause painful blisters. Both start as a red macule, which soon becomes raised and forms a vesicle. Pain preceding the appearance of the skin lesions is a very important clue to this diagnosis.

Herpes simplex causes small, closely grouped vesicles on a red base and these can be located anywhere on the body, not just the most common sites (lips or genitals).

Herpes zoster lesions are more linear and restricted to one side of the body following a dermatome. In immunosuppressed people or patients on chemotherapy, this condition can involve several dermatomes.

Herpes simplex can be treated with either topical or oral aciclovir. Frequent recurrences may need an extended course of oral aciclovir. In immunosuppressed patients, herpes simplex can become generalised and may be life-threatening. In this situation, hospital admission and IV antivirals will be necessary.

Treating herpes zoster with antivirals has been shown to reduce the acute pain, virus shedding, rash and the incidence and severity of post-herpetic neuralgia.2

Eczema herpeticum

Eczema herpeticum is a condition with a somewhat misleading name, as it suggests there has to be eczema, but any skin problem that breaches the skin barrier can be complicated by herpes simplex (although eczema is the most common cause of barrier dysfunction). Often mistaken for impetigo, it consists of small, very even, punched-out blisters, which look as if someone has tried to take shallow punch biopsies.

It can become secondarily infected with bacteria. If a skin problem suddenly deteriorates, especially if the patient is complaining of pain, it is important to consider giving oral aciclovir – topical treatment will not be enough.

Herpetic whitlow

A herpetic whitlow is a vesicular infection around the nail fold caused by herpes simplex. This is a painful condition and causes swelling of the digit. The thumb and index finger are most commonly affected. It requires topical antivirals if mild or oral antivirals if more severe, very painful or recurrent.


Chickenpox initially presents with fever and crops of red macules that progress over a matter of hours to papules and then vesicles, which take a few days to dry up and form a scab.

Hand, foot and mouth disease

Hand, foot and mouth disease is a mild, short-lasting viral infection mainly affecting young children. It gives small, oval-shaped pearly grey blisters on the hands and feet and in the mouth, and is very infectious. It is caused by an enterovirus, usually Coxsackie A16. These small blisters resolve within a week, without leaving scars.


Orf is a parapoxvirus contracted from goats and sheep. It is common in sheep farmers and those working in the meat industry. Children can acquire it from bottle-feeding lambs or playing in an infected field.

It presents with a small, firm, red or bluish-red papule, usually on the hand, which progresses into a blister that is often quite purple. This can grow to a large lesion 2-3cm in diameter. It is self-healing in about six weeks but there may be a need to treat any secondary bacterial infection.

Orf: papule progresses to a blister, which can be quite large (Photograph: ISM/Science Photo Library)


Cellulitis can present with blistering of the affected skin along with the classic signs, which are sudden development of fever, feeling unwell, one-sided redness, swelling, tenderness and increased warmth.

The usual causative organism is Streptococcus, and penicillin V and clarithromycin are the antibiotics of choice, at higher doses than normal. Severe cases will require hospital admission.

If the redness is bilateral, has been developing slowly and is not acute, it is more likely there is another diagnosis, such as infected eczema, which is a frequent cause.

Bullous impetigo

Bullous impetigo is a less common form of impetigo that can affect intact skin and is caused by exfoliative toxins of Staphylococcus aureus. The exotoxins produce loss of adhesion in the superficial dermis, causing fragile blisters that often rupture to give superficial erosions.

Coagulase-positive group II Staph aureus, most often phage type 71, is the predominant causative organism and is the same strain that causes staphylococcal scalded skin syndrome.

Bullous impetigo is treated in the same way as non-bullous impetigo, with the use of antiseptics, topical or oral antibiotics and dressings.

Bullous impetigo: blisters may rupture to give superficial erosions (Photograph: Dr P Marazzi/SPL)

Eczema and dermatitis

Pompholyx eczema

Eczema on the palms and soles is more likely to blister and the classic presentation of pompholyx eczema is small, extremely itchy vesicles along the sides of the fingers.

The differential is palmoplantar psoriasis, which gives bigger, yellow pustules with some older brown ones that are painful rather than itchy. The patient with psoriasis is likely to be a smoker or ex-smoker.

Pompholyx eczema requires potent topical steroids. Dilute potassium permanganate soaks can be very useful in the acute stage to calm the itch and prevent bacterial infection. The skin peels after the vesicles dry up.

Discoid eczema

This type of annular eczema is often mistaken for psoriasis because it has a well-demarcated border that is more pronounced than is usual in eczema.

It is more common in winter, often affects the lower legs and can be triggered by an insect bite or minor injury. There can be grouped vesicles and it can be very itchy. Strong topical steroids may be required to bring this condition under control.


Nickel allergy can be acute and may present with small blisters, especially on the ears from wearing earrings, or around the umbilicus from belt buckles. Hair dye allergy can cause dramatic blistering on the face. Avoidance of the allergens will prevent recurrence. This is particularly important for hair dyes, where repeat eruptions can be extremely severe.

Plant dermatitis

Plant dermatitis can be due to direct contact with a plant, or after sun exposure on the area of skin that touched the plant.

The distribution of the blisters in plant-induced dermatitis is usually linear or streaky and asymmetrical.

Plants that can cause photocontact dermatitis are the citrus family, celery, parsnip, fig and giant hogweed, which all have high levels of furocoumarins, a naturally occurring psoralen. Squeezing limes outside on a sunny day can cause very dramatic blistering. Phytophototoxic reactions have occurred after eating parsnip or celery soup and then being out in the sun.

Oedema blisters

This type of blistering is underdiagnosed but is a common cause of lower leg blistering and is due to the rapid development of oedema. These can be large, unilocular, clear blisters and are associated with heart failure and venous insufficiency. It is most important to determine and treat the underlying cause, as well as to protect the blisters to prevent secondary infection.

Nutritional causes

Rarely, blisters can be caused by nutritional deficiency. Acrodermatitis enteropathica is a genetic disorder that causes malabsorption of zinc. In the infant, a perioral and perianal rash develops, plus blistering of the fingers, toes and ears, along with diarrhoea. Oral zinc improves the skin within days.

In adults, zinc deficiency can occur as a result of alcoholism, severe inflammatory bowel disease and after bariatric surgery.

Drug-induced blisters

Drug eruptions come in many different forms, including bullous eruptions. Drugs that can cause blistering are barbiturates, furosemidenalidixic acid and penicillamine.

Fixed drug eruption

Fixed drug eruption is an uncommon condition where dusky red or purple plaques occur when the causative drug is taken. The timescale between taking the drug and the lesion flaring up is 30 minutes to eight hours.

Initially, there is a single plaque, but with repeated episodes, the plaque expands and can multiply. The lesions tend to blister, with pigmentation on clearing.

Many drugs can cause this, but oral antifungals, paracetamol, NSAIDs, aspirin and antibiotics are the most common. Sites affected are the mouth, anogenital region, hands and feet.

Cause   FeaturesSiteTreatment
Friction blistersOften due to footwear, gripping tools or sports equipmentSoles and palmsDrain fluid from blister with sterile needle if large or bothersome, leaving roof of skin to protect the base
Insect bitesLinear or groupedLimbsAntihistamines and topical steroids
Scabies in babies and infantsItchy vesicles, can look like eczema

Hands and feet

Topical scabicide all over; repeat week later; treat all household contacts on same day
Herpes simplex

Pain precedes small groups of vesicles

Lips, genitals and buttocks most common

Topical aciclovir if mild; if recurrent, widespread or other health problems, use oral aciclovir
Herpes zosterPain precedes vesiclesAny dermatome Oral antivirals
ChickenpoxMacule to papule to vesicle within hoursMost prominent on trunk and face Consider prompt oral antivirals in those aged over 14 years, especially if other health problems, and in newborns or pregnant women
Hand, foot and mouth diseaseSmall, oval, pearly grey blistersAcral distributionAnalgesics, keep the blisters intact to prevent viral spread
OrfFarm workers, vets, meat industry workersHand or arm, occasionally faceTreat if secondary bacterial infection; usually resolves within six weeks 
Pompholyx eczemaVery itchyHands and feetPotent topical steroids, potassium permanganate soaks; may require oral antibiotics
Discoid eczemaVery itchyLimbs, especially legsPotent topical steroids
Plant dermatitisLinearArms, legs, trunkTopical steroids or oral steroids if severe
Oedema blisters

Unilocular, clear blisters

Lower legsTreat oedema; bed rest
Zinc deficiencyInfants, adults with alcoholism, after bariatric surgery or severe inflammatory bowel diseasePerioral/perianal rash, blisters on fingers, toes and ears, diarrhoeaOral zinc supplementation
Fixed drug eruptionAnnular Lips, genitals, lower abdomen commonExclude most causative drug 

  • Dr Elizabeth Ogden is associate specialist in dermatology, Lister Hospital, East and North Herts NHS Trust

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1. Dupuy A, Dehen L, Bourrat E et al. Accuracy of standard dermoscopy for diagnosing scabies. J Am Acad Dermatol 2007; 56: 53-62.

2. Pavan-Langston D. Herpes zoster antivirals and pain management. Ophthalmology 2008; 115(2 Suppl): S13-20.

Further learning

These action points may provide opportunities for further CPD on this topic

  • Present a summary of blistering conditions to colleagues
  • Look up photographs of blistering conditions to familiarise yourself with the different presentations
  • Produce a patient factsheet on blistering conditions

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