Reasoning GP · Algorithm · 1-page summary
Anal itchiness (pruritus ani)
For: adults and children with perianal itch in primary care. Not for: the full management of threadworm, haemorrhoids, psoriasis or lichen sclerosus (use their own pages).
Core rule: examine every patient. A persistent, one-sided, crusted, pigmented, indurated or ulcerated plaque may be anal neoplasia or Paget disease: biopsy it rather than keep treating it as eczema.
0Stop — call 999 now — rare in pruritus ani
- After a mebendazole dose: swelling of the lips, face or tongue, difficulty breathing or wheeze, or collapse (anaphylaxis) → 999
- Otherwise the danger is a missed cancer, systemic disease or safeguarding concern: screen with block 2 first.
1Triage by pattern — history first
| Pattern | Think of |
|---|---|
| Nocturnal, child or household | Threadworm |
| Daytime + products | Contact or irritant dermatitis: wipes, soaps, haemorrhoid creams, antiseptics |
| Constant, skin change | Eczema, lichen sclerosus, psoriasis, Paget disease |
| Soiling, loose stool | Haemorrhoids, fistula, loose stool; diet triggers |
| Generalised itch | Liver, kidney, lymphoma, polycythaemia, thyroid |
2Screen — one row is enough
- Itch with bleeding, altered bowel habit, iron-deficiency anaemia or abdominal mass → FIT per NG12 age/symptom criteria; FIT ≥10 µg Hb/g → Suspected cancer pathway
- Rectal mass, or unexplained anal mass or ulceration → Suspected cancer pathway, no FIT.
- Persistent asymmetric, scaly, crusted, pigmented, indurated or ulcerated plaque, especially treatment-resistant → Urgent biopsy via dermatology, colorectal or anogenital neoplasia pathway.
- Generalised itch + new jaundice → Same-day assessment, LFTs and bilirubin; aged 40+ → NG12 pancreatic pathway.
- Child with warts, genital lesions, trauma, bleeding, disclosure or STI → Same-day safeguarding lead or paediatrician, and children's social care.
- New bleeding, abscess or severe pain, fast-spreading skin change, new lump or ulcer, fever, weight loss → Same-day GP
3Assess — with consent ± chaperone
☐ Perianal inspection: satellite lesions, white atrophic or glazed red plaque, warts, ulcer ☐ Genitalia if lichen sclerosus, candida or STI possible ☐ DRE in adults with bleeding, pain, mass, altered bowel habit or discharge ☐ Elbows, knees, scalp, nails ☐ Every cream, wipe and haemorrhoid product used
No routine bloods for localised itch with a normal examination. HbA1c if candida is recurrent or extensive; tape test if threadworm is uncertain (not stool microscopy); FBC/ferritin, U&E, LFTs, TFTs only if itch is generalised or systemic.
4Classify — only if the screen is negative
- Threadworm — nocturnal itch, children, household affected → treat household (block 5).
- Idiopathic / soiling — normal skin or excoriation; coffee, loose stool, haemorrhoids, sweating. Commonest in adults → hygiene + barrier; treat the cause.
- Contact dermatitis — weeping, ill-defined rash; wipes, soaps, anal creams → stop the product; patch testing if it persists.
- Candida — satellite lesions; antibiotics, diabetes, immunosuppression → topical imidazole.
- Psoriasis (glazed plaque, no scale) or lichen sclerosus (white atrophic plaque, fissuring) → short mild/moderate steroid for psoriasis; clobetasol only for confirmed lichen sclerosus.
- Uncertain or not improving → reassess and biopsy; never continue empirical creams indefinitely.
5Treat today — doses: NICE/SPC, BNF, local formulary
- Everyone: water-only washing, pat dry; no soap, wet wipes or talc; cotton underwear; short nails; zinc oxide or petroleum jelly barrier after washing and defecation.
- Threadworm: mebendazole 100 mg single dose, repeat once after 2 weeks (local guidance); treat household at the same time. Licensed from 2 years; 6 months–2 years off-label. Under 6 months and pregnancy: hygiene for 6 weeks first.
- Clear inflammation (infection and suspicious lesions excluded): consider hydrocortisone 1% once or twice daily for up to 7–14 days. Candida: topical imidazole, e.g. clotrimazole 1%.
- Diet: individual 2–4-week trial of reducing suspected triggers (coffee, tea, cola, alcohol, spicy food). Sedating antihistamines are not antipruritics; avoid in older adults.
6Refer routinely
- Dermatology: no meaningful improvement after 4–6 weeks; suspected lichen sclerosus or psoriasis; patch testing; undiagnosed skin condition.
- Colorectal: haemorrhoid-related soiling or fistula. GUM: new, multiple, recurrent or atypical warts; STI; HIV with perianal lesions.
- Review at 2–4 weeks if treatment started or symptoms significant.
7Never reassure by
- “Eczema” that keeps failing treatment: biopsy it.
- Bleeding put down to haemorrhoids without examination.
- A low, unavailable or unreturned FIT when concern remains.
- Lichen sclerosus in a child: it does not exclude abuse.
- Repeated mebendazole for itch that does not settle: re-examine.
- A history taken without looking: inspect every patient.
8Safety-net — say it, then document it
999 “Call 999 if, after the worm tablet, your lips, face or tongue swell, you wheeze or struggle to breathe, or you collapse.” Same day “Contact us today for new bleeding from the back passage, a new lump or sore, severe pain or an abscess, a rash spreading quickly, or fever, weight loss or swollen glands.”
Review: not clearly better by 4–6 weeks → come back to be re-examined, as a biopsy may be needed. Remote: book face to face; the diagnosis needs perianal inspection.
✓Safe to leave primary care only if — all five, documented
No block 0–2 row applies
Perianal skin inspected; DRE if bowel symptoms
All creams, wipes and products reviewed
Cause named or uncertainty stated; household treated if threadworm
Review booked; safety-net given
Summary of the full Reasoning GP anal itchiness algorithm, which holds the history, examination, differential and evidence. Sources: NICE NG12 (updated April 2026); PCDS pruritus ani; BAD lichen sclerosus guideline (2018); IUSTI-Europe anogenital warts; local antimicrobial guidance (threadworm); MHRA. Clinical reference — follow local safeguarding and referral pathways and check doses: NICE/SPC, BNF.