Kencing lipas beetle rash on the eyelid: Paederus dermatitis and what to do if it gets in the eye

You wake up and one eyelid is swollen, with a red, stinging streak that was not there last night. In Malay it is "mata kena kencing lipas" or "mata bengkak kena kencing lipas", and Malaysians also call the insect semut charlie or semut kayap. The cause is a small beetle that is easy to miss. This piece explains the rash, how to tell it from a stye, an eyelid infection, shingles and ordinary contact dermatitis, what to do in the first minutes, and the signs that mean an eye doctor the same day.

What is "kencing lipas" on the eyelid, and does the beetle bite?

It is a burn-like skin reaction to a rove beetle of the genus Paederus, and the beetle does not bite or sting. A Malaysian case series says it releases toxic haemolymph, its body fluid, only when it is crushed on the skin. The toxin is called paederin, and the condition is Paederus dermatitis, known in Chinese as 隐翅虫皮炎.

The beetle is small. The same Malaysian series, from student hostels in Selangor, describes an adult of 7 to 10 mm with a black head, an orange body and metallic blue wing cases. It is active at night and drawn to light. The authors note that students there opened windows for air and then switched on fluorescent lights to study, which brought the beetles in, and DermNet says the same about open windows and fluorescent lights. The Selangor series recorded 360 cases in one year at one student health centre, most from a hostel beside an oil palm plantation.

Why does the rash appear a day later, and what does it look like?

The toxin does not hurt on contact, so the skin reacts hours later. DermNet says a blistering rash occurs 24 to 48 hours after brushing against or crushing the beetle on the skin. Streaky redness comes first, then blisters and pustules around days 2 to 4, often with a burning feeling.

The shape is the clue. DermNet describes streaky or linear lesions on exposed skin, and "kissing lesions" where two skin surfaces touch, such as the armpit or groin. A clinical image report in the Oman Journal of Ophthalmology describes the typical picture as a linear red plaque with small blisters on exposed sites, with itching and burning, followed by crusting and peeling. It is also called "night burn" or "wake and see" disease, because people notice it on waking. In the Selangor series most students noticed the rash when they got up, and the face, neck, shoulders and arms were the usual sites.

I would pay attention to that streak shape more than to the colour.

How is it different from a stye, preseptal cellulitis, shingles or contact dermatitis?

A beetle rash is a streak or patch of burning, blistering skin that follows contact, while the others have their own patterns. DermNet lists herpes zoster, allergic and irritant contact dermatitis and other conditions among the lookalikes, and the Oman report lists herpes zoster ophthalmicus, impetigo and preseptal cellulitis. The Selangor series reports a student who was prescribed an antiviral medicine for what proved to be Paederus dermatitis.

A stye is one tender lump at a lash root or inside the lid. The NHS describes it as a small, painful lump on or inside the eyelid that should go away within a week. If your problem is a single lump, read my page on the stye.

Preseptal cellulitis, infection of the eyelid in front of the orbital septum, is a hot, red, swollen lid. Moorfields describes the milder form as having no raised temperature and normal vision. A beetle rash can look similar when the lid is badly swollen, which is why the page on preseptal cellulitis is worth reading as well.

Shingles is on one side of the body only, according to the NHS, and can begin with tingling or pain before the rash. The NHS says a rash on or near the eye is a reason to ask for an urgent GP appointment or call NHS 111, and so is any change in vision. Contact dermatitis, in the NHS description, is itchy, blistered, dry and cracked skin within hours or days of touching an irritant or allergen. The lash glue and cosmetic version is in my page on allergic eyelid reactions.

DermNet lists the features that point to the beetle: irritation confined to exposed skin, kissing lesions, a warm or rainy season, and other people with similar lesions. A new streak after a night with beetles in the room is enough to think of it. If you are not sure which of these you have, the broader guide to a suddenly swollen eyelid sets out the urgent signs.

What is "Nairobi eye", and when has the toxin reached the eye itself?

Nairobi eye is the name for Paederus dermatitis around the eye, with or without inflammation of the eye surface. DermNet describes periocular dermatitis and keratoconjunctivitis, inflammation of the conjunctiva and cornea, under that name. The Oman report says the eye involvement is usually on one side only.

It usually happens when the toxin is carried there. The Selangor authors say ocular involvement is usually secondary to rubbing the eyes with hands contaminated with paederin, and list oedema, conjunctivitis and excess tearing as common. The Oman report adds that the periocular lesion can come from direct contact or from the toxin carried on the fingers from elsewhere on the skin. That is why the advice is not to rub.

There is some reassurance in the same report. It says the toxin is a weak base that cannot penetrate the cornea and conjunctiva well, so the damage is limited. The healing times it gives are about 10 days to 2 weeks for the lid and conjunctiva, and up to 50 days when the cornea is involved. It also lists post-inflammatory pigmentation and temporary blindness among the complications.

The practical meaning for you: a swollen, blistered lid on its own is a skin problem. A painful or light-sensitive eye, a change in sight, or an eye you cannot keep open is an eye problem. The NHS lists each of those after an eye injury as a reason to go to A&E, and I would treat a beetle splash the same way.

What should I do in the first minutes, and what should I leave alone?

Do not rub, wash the skin with soap and water, and cool it. DermNet advises removing a beetle from the skin without crushing it, washing the skin that touched it with soap and water, and using a cold wet compress. The Selangor authors say washing the exposed skin with soap and water immediately can greatly diminish the effect of paederin.

Brush the beetle off with a tissue or a piece of paper. Then wash your hands before you touch your face again, because the toxin travels on fingers. Soap is for the skin, not for the eye itself. If you think something has got into the eye, the NHS advice for something in the eye is to run plenty of clean, not hot, water over the eye, for at least 20 minutes, and not to touch or rub it. That page is about eye injuries in general, not about beetles.

Leave the home remedies out. The Selangor authors report that students who used calamine lotion found it had little effect, and they cite an East African report in which toothpaste and mud were ineffective. DermNet lists infection and skin breakdown among the complications, so leave the blisters alone.

What does the doctor check, and what treatment is used?

The diagnosis is mostly clinical, which means it rests on the story and the look of the skin, as DermNet and the Oman report both say. The history matters: whether there was a beetle, a night with open windows and lights, and whether anyone else at home has the same streaks. The Oman report names three places the toxin can affect: the lid, the conjunctiva (the thin clear layer over the white of the eye) and the cornea, the clear window at the front.

Treatment for the skin is simple. DermNet lists washing, a cold wet compress and a topical steroid, which is a cream that damps inflammation, and says oral antibiotics are used when there is a secondary bacterial infection. The Oman case report used cold compresses, an oral antibiotic, an antihistamine, a painkiller and a steroid and antibiotic cream, and the lesions healed in 10 days with mild pigmentation. Because a steroid near the eye needs care, my page on steroid cream near the eye explains why a doctor should choose it.

Marks can last. In the Selangor series some people kept linear scars and darker patches after treatment. DermNet says the rash can take several weeks to resolve and the pigmentation may last several months. If a scar tightens or pulls the lid, or a pigment change has not faded, that is a reason for an eyelid assessment.

How do I keep the beetle away from my eyes?

Brush it off, never crush it, and give it less reason to come in. DermNet recommends insect-proof netting at night, light sources that do not emit ultraviolet, turning lights off while sleeping, and washing any skin that has touched a beetle. The Selangor authors recommend window mesh.

The Malaysian series links the cases to the rainy season and to places near plantations, wetlands and paddy fields, though it also notes beetles in built-up areas.

For a child, Dr Chan Li Yen at Little Eyes 101 has written about the tomcat beetle near a child's eye, with the steps that suit children.

The sequence to remember is contact, a quiet day, a burning streak, and an eye that is seen the same day if it is involved. For more on lids that swell for other reasons, see the hub on what makes eyes look tired and the page on upper, lower, one or both swollen eyelids.

The wider guides to lumps and lashes and to eyelid position and droop cover the conditions that are sometimes mistaken for a beetle rash.