A problem that occurs during or after a trip does not necessarily need to have a causal connection with that trip.

• Bathing too frequently is a common cause of generalised pruritus in tourists and expatriates. Diseases such as atopic eczema, xerosis, psoriasis, urticaria, ichthyiosis, lichen planus and pityriasis rosea of Gibert in practice seldom raise diagnostic problems and are not considered further here. Diagnosis of dermatitis herpetiformis (Duhring-Brock disease) can be more difficult.
• AIDS is frequently associated with recurrent and often chronic fever, together with persistent diarrhoea and pruritus that is difficult to treat. The possibility of Norwegian scabies as well as of side effects of medication should be considered.
• Onchocerciasis is the filariosis that is pre-eminently accompanied by chronic pruritus. Eye lesions, subcutaneous noduli and enlarged lymph nodes are relevant symptoms. The detection of microfilariae will confirm the diagnosis. Mansonella streptocerca can likewise cause pruritus (milder symptoms). Other filarioses (loasis, bancroftosis) can likewise be accompanied by pruritus, though the association here is not so strong.
• West African trypanosomiasis is characterised dermatologically by transient erythema (trypanids) and by recurrent pruritus. Fever, splenomegaly and enlarged cervical lymph nodes will direct the diagnosis. Serology should be carried out and trypanosomes should be searched for.
• Persistent insect bites are responsible for intense pruritus, but the pruritus tends to be localised at the bites. Delayed hypersensitivy reactions to insect allergens play a role in this condition.

• Scabies. The small itch-mite, Sarcoptes scabiei, lives in the epidermis. Transmission takes place during close physical contact. After a first infection there is a long incubation period (3-6 weeks). This becomes shorter upon repeated infections. Norwegian scabies also occurs at locations other than the classical scabies sites.
• Diagnosis of trombiculosis (skin irritation due to Trombicula autumnalis) can be difficult. Larvae of these harvest mites are responsible for the itching, but stay for only a short time on the skin. They usually produce discomfort during country walks in the warm months.
• Cheyletiellosis (irritation of the skin by animal fur mites). A number of species of the Prostigmata order Cheyletidae (e.g. Cheyletiella parasitovorax, C. yasguri, C. blakei) can cause a severe prurigo characterised by small erythematous spots with vesicular (blister-like) centres. Itching occurs after contact with infested domestic animals such as rabbits, dogs and cats.
• Various mites belonging to the order Astigmata (e.g. Tyrophagus sp, Acarus sp, etc.) are very small mites found in hay and stored food. They can cause pruritic dermatitis.

• Lepidoptera. Skin contact with urticarial caterpillar hairs carried by the wind can cause a generalised pruritus, occasionally accompanied by dyspnoea. During a caterpillar plague this can have serious consequences.
• Seafood. Ciguatera poisoning occurs after eating fish that contain toxins of certain dinoflagellates (e.g. Gambierdiscus toxicus). The fish have a normal appearance and normal taste. Abdominal pain, diarrhoea, nausea and vomiting occur soon after the meal. These are accompanied by headache, muscle pain, paresthesias and pruritus. However, itching is usually not the dominant symptom. Scombroid intoxication due to consumption of stale fish such as mackerel, tuna or bonito can cause an itching accompanied by abdominal pain and facial flush (histamine-like toxin). The symptoms usually disappear spontaneously after 24 hours. Urticaria occurs frequently after consumption of various crustaceans (e.g. shrimp, lobster, crayfish). The pruritus is mediated via IgE (a RAST test can be carried out if in doubt).
• Psychogenic pruritus and parasitophobia can be particularly obstinate. Psychiatric advice is frequently necessary.
• Cholestasis, with or without icterus (jaundice), is a major cause of itching. Intrahepatic cholestasis can occur during pregnancy or medication (e.g. testosterone). Cholestasis is also present in bile duct obstruction. Pruritus in primary biliary cirrhosis can sometimes be very pronounced and occur very early on in the illness.
• Chronic uraemia is frequently accompanied by itching, even if no uraemic frost is present. Kidney failure causes phosphate retention with hypocalcaemia. This can result in secondary hyperparathyroidism. This may also play a part in the maintenance of pruritus. A simultaneous polyneuropathy makes the clinical condition worse.
• Iron deficiency anaemia. Pruritus occasionally occurs here, though this is rare and the other signs of anaemia are foremost. Fatigue with accelerated respiration, rhagades, brittle flat finger- and toenails and pale conjunctivae occur.
• Endocrine abnormalities such as hyperthyroidism and diabetes mellitus are associated with an increased risk of pruritus. Hyperthyroidism can occur as a result of prolonged use of iodine for disinfection of water.
• Medicinal. Use of morphine (frequently) and cocaine (occasionally) can have pruritus as a side effect. This is not due to allergy and there is no erythema. The aetiopathogenesis is different from that of phototoxicity (e.g. with tetracyclines) and medication induced rashes. Individuals with a dark skin quite often exhibit pruritus after ingestion of chloroquine (chloroquine is melanotropic).
• Neoplastic. Pruritus can occur with lymphomas, particularly Hodgkin’s disease. It is also a paraneoplastic symptom of other deep tumours.
• Carcinoid tumours arise from neuroendocrine cells, most frequently from enterochromaffin cells in the gastrointestinal system. They cause a characteristic symptomatology (carcinoid syndrome), with flushing, diarrhoea and cardiac valve disease (such as pulmonary stenosis). Hypotensive attacks and urticarial episodes with itching occur. Mild pellagra can appear. Serotonin (5-HT, 5-hydroxytryptamine) is metabolised to 5-hydroxy-indolacetic acid (5-HIAA). It is important to follow a correct diet before carrying out a 24-hour urine collection for measurement of this metabolite. Diagnosis is often difficult. Radioisotopic scanning with meta-iodobenzyl guanidine (MIBG-scan) or with octreotide is sometimes carried out.
• Systemic mastocytosis (urticaria pigmentosa) is a rare disease. Recurrent cutaneous flushing, headache, diarrhoea and abdominal pain, cardiac palpitations and brown skin pigmentation occur. Pruritus and local urticaria after physical trauma can occasionally be elicited by local rubbing on the skin. Complications such as malabsorption or periportal fibrosis sometimes occur, with secondary portal hypertension and ascites. Mastocytosis can also be restricted to the skin.
• Polycytaemia vera. Itching frequently occurs in Vaquez’ disease. The diagnosis can be suspected from a full blood count. The difference from secondary polycytaemia due to chronic hypoxia is usually obvious. An increased haematocrit can occasionally result from the abnormal production of erythropoietin, e.g. by a kidney tumour.

The cause of pruritus may be related to a recent trip. There is however often no aetiological connection between a trip that has been undertaken and occurrence of pruritus (incidental association).

Scabies, prickly heat (miliaria rubra) and insect bites are the most frequent causes of pruritus.

Sweat erythema (miliaria syndrome, prickly heat, bourbouille) is caused by irritation of the skin around the sweat glands during heavy perspiration in a warm, often humid environment. The disease is characterised expressed by a rash with multiple small blisters (clogged sweat glands). If there is no inflammation this disease is called miliaria crystalina. The sweat glands can secondarily become inflamed and additionally infected (miliaria pustulosa). This can resemble folliculitis. Miliaria rubra is accompanied by spots and blisters on and around the sweat glands with concomitant erythema and severe itching inflammation of the skin. Preferred locations are the flexor areas of elbows, knees, groins and armpits. If this occurs repeatedly, miliaria profunda can occur. Local hygiene and avoiding excessive washing of the skin are important. The condition is usually self-limiting (the irritation diminishes or disappears as soon as the sweat glands are no longer clogged).

Bites by fleas, sandflies, Culicoides species, Aedes sp and Mansonia mosquitoes are especially notorious among insect bites. Itching can persist for weeks. Hypersensitivity reactions with pronounced small to large blister lesions are not unusual here (culicosis bullosa). Bites by bedbugs (Cimex sp) frequently occur. The disease characterised by severe skin reactions to repeated Phlebotomus sp bites is known in the Middle East as "harara". The lesions are sometimes sustained by chronic scratching.

The possibility of Enterobius vermicularis (pin worms) must be suspected here. The faeces often contain no detectable ova, though the eggs of the parasite can be detected with an adhesive Scotch tape test of the perianal skin.

Active mobile proglottids of Taenia saginata (beef tapeworm) may occasionally spontaneously crawl out of the anus, resulting in local pruritus.

In cases of infestation with Strongyloides stercoralis, larvae of the worm will occasionally cause a perianal reinfestation. This is apparent as a superficial migrating red stripe.

Irritation of the perianal skin can occur due to persistent diarrhoea (Giardia, Campylobacter). Haemorrhoids, anal fistulae, eczema of the perianal area and perianal fistula with repeated secretion of moisture can give rise to chronic itch. This itch is occasionally sustained by chronic scratching, resulting in lichenification of the skin. Dermatomycosis of the perianal region as well as a malignant tumour should be ruled out. The gluteal fold is one of the preferred sites where psoriasis occurs (psoriasis intertriginosa). Hydradenitis suppurativa (pilonidal sinus) can occur in hairy individuals (often Caucasian men after a trip on bumpy roads with prolonged sitting in a bad seat: "jeep-disease").

Lichen planus can cause anal itch (both the anal and the oral mucosa can be affected by this disease). Typical skin lesions and the presence of Wickham striae on skin lesions or on the oral mucosa suggest the diagnosis.

Pubic lice (Phthirus pubis) are a frequent cause of genital itch. Scabies may be accompanied by itching on the genitals and by the formation of scrotal noduli.

Dermatophytes, Candida and erythrasma are important causes of perigenital itch. Diabetes mellitus must be taken into account. Diagnosis of kraurosis vulvae or of psoriasis is usually clinically obvious.

Lichen planus is an itchy papulosquamous condition with a predilection for wrists, calves, lower back and genitals. The lesions consist of glossy purple polygonal papules. Upon inspection one looks for a fine network of small lines (Wickham striae) on these papules. Lesions sometimes also occur on the scalp. The oral mucosa can be affected.

Head lice (Pediculus humanus capitis), psoriasis, tinea capitis and seborrheic eczema are the principal causes of pruritus of the scalp. Lichen planus lesions can also occur on the scalp. Normally, secondary syphilis causes non-itching scalp lesions, such as alopecia, but it is wise to test for lues in case of baffling clinical presentations.

A larva migrans cutanea is characterised by a slowly moving, chronic erythematous track, often strewn with papules or vesicular papules. The lesions are usually on the foot, but localisation on other body parts also occurs. A larva currens (Strongyloides stercoralis) is recognised as a rapidly moving, transitory urticarial lesion. Subcutaneous gnatostomiasis (Gnatostoma spinigerum) and migration of an adult Loa loa (filariosis) can produce a similar effect.

Pruritic berloque dermatitis (contact dermatitis due for example to cosmetics or perfumes) can occasionally mimic larva cutanea migrans.

Suspect aquagenic pruritus, but also planula larva dermatitis (microscopic larvae of saltwater Cnidaria) and cercarial dermatitis (swimmers’ itch after contact with fresh water), due to penetration of cercaria into the skin.

Dermatitis caused by fireworms (Eurythoe complanata, Annelida) or irritation by mature coelenterata (Cnidaria) such as fire coral [Millepora tenera], jellyfish (Scyphozoa) or Siphonophora (e.g. Portuguese Man-of-War [Physalia physalis]) are obvious from the history of the condition. Certain seasnails (Nudibranchia, seasnails) are capable of ingesting the nematocysts of their prey intact and even of using them for their defence. Pain rather than itch is foremost here.

Caisson disease due to rapid decompression after a dive can initially result in itching and a mottled appearance of the skin. These symptoms can precede more serious problems (abdominal pain, transverse myelitis, lung embolism due to nitrogen gas). Aseptic bone necrosis is a later complication.

In addition to cosmopolitan diseases such as eczema, lichen simplex, neurodermatitis and dyshidrosis (pompholyx), we mention insect bites (flea bites, Aedes sp., etc.) and contact dermatitis. Phytodermatitis can be a consequence of contact with various plants, such as poison oak or poison ivy. The plant sap of certain spurge or milkweed varieties (Euphorbia sp.) can cause an intense pruritic dermatitis.

Hairs of bird spiders and of certain caterpillars can cause considerable local pruritus. The oak processionary caterpillar (Thaumetopoea processionea), Euproctis chrysorrhoea and Orgyia antiqua are typical examples of the latter. Bites by fire ants (Solenopsis sp.) are rarer. Such bites are very painful. Contact with blister beetles such as Paederus sp. and cantharids (Spanish fly) can cause irritating lesions. Myiasis (infestation by fly larvae such as Cordylobia anthropophaga in Africa or Dermatobia hominis in South America) can initially result in an itching pseudofurunculosis.

When people walk barefoot or sit down on an ancylostoma-infested place, so-called "ground itch" can occur. Penetration of hookworm larvae causes temporary local pruritus. Infestation with sand fleas (Tunga penetrans) will produce pruritic lesions.

Early cutaneous anthrax lesions can be pruritic.

The limb where a rabid animal has bitten and where rabies virus was inoculated into the skin, can become extremely pruritic before the cerebral signs dominate. Excoriation of the bite site due to repeated scratching is not exceptional.

Pruritus of various aetiologies, e.g. scabies, streptocercosis, onchocerciasis, polycytaemia vera (Vaquez' disease), will be worse at night or will be elicited by warmth.

Bites by avian mites are a very typical, though rare cause of nocturnal itch. Birds can be parasitized by various mites: Dermanyssus gallinae, D. hirundinis, Ornithonyssus sylviarum (the northern fowl mite) etc. Dermanyssus gallinae (the chicken mite) is a frequent ectoparasite of birds. When there is a bird’s nest close to a house (under the eaves or loose tiles, on the balcony or in the loft, or there are pet birds such as canaries etc. in an aviary), the mites can get into the house and suck blood at night. This will happen when their natural host is absent (when young birds fly away, old nests). This nocturnal bloodsucking causes a severe nocturnal pruritus, papular and even vesicular erythema (so-called pigeon scabies or gamasoidosis). The face is usually spared. The tiny mites can occasionally be found on the bed and on the mattress. Identification of the mites will lead to the diagnosis. As the mites can survive for several months without a blood meal, the house should be treated with insecticides (acaricides). After fumigation nearby birds’ nests should be removed and bird netting should be put up. As the mites live on birds for only a short time, domestic birds do not have to be removed or even treated.

Animals can be infested by various fleas. The diagnosis is no problem. On the other hand animals such as dogs, cats and rabbits often have infestations with Cheyletiella mites. Domestic pets exhibit few or no symptoms at all, but in humans the mites cause a pruritic dermatosis. Domestic pets must be treated.

Certain mites (Neotrombicula autumnalis) elicit autumnal erythema (trombiculosis or trombidiosis) after a visit to meadows or forests during the summer or autumn. These harvest mites are not vectors of pathogens, but elicit a temporary pruritic dermatitis. The pruritus is most pronounced on places where clothing is in close contact with the skin. The mite itself, 200 µm in length, is of an orange-red colour and clamps itself firmly to grass blades, usually in areas with a clay or loess soil. It is seldom found on humans (it gets scratched off). To prevent contact with these mites it is advisable to keep the grass short in gardens in areas with these soil types.

When you go walking in the summer in areas where many oaks grow you can come into contact with the stinging hairs of the oak processional caterpillar. Severe itching, throat- and nasal pain, dyspnoea and dysphagia can occur.

Stinging by nettles in usually obvious. One also has to keep the possibility of phytodermatitis and phytophotodermatitis in mind after a walk in a meadow.