What causes intense anal itching?

Causes of Intense Anal Itching

Intense anal itching (pruritus ani) is most commonly caused by inadequate hygiene, minor fecal incontinence, or perianal dermatitis, but can also result from hemorrhoids, infections, skin conditions, systemic diseases, or medication side effects. 1

Primary Causes

• Hygiene-related factors:

  • Inadequate cleaning after bowel movements
  • Excessive cleaning with soaps/irritants
  • Moisture retention in the perianal area
  • Fecal soiling (most common primary cause) 2

• Dietary triggers:

  • Caffeine
  • Spicy foods
  • Citrus fruits
  • Tomatoes
  • Chocolate
  • Alcohol 3, 4

Secondary Causes

Local Anorectal Conditions

• Hemorrhoids: Prolapsing hemorrhoids can cause itching due to mucus secretion and irritation 1
• Anal fissures: Cause pain and itching, especially during and after defecation 3
• Fistulas: Result from chronic infection of anal glands 3
• Skin tags: Can trap moisture and fecal matter

Infections

• Fungal infections: Candida species (especially in diabetics or immunocompromised patients)
• Parasitic infections:
  • Pinworms (Enterobius vermicularis) - particularly common cause of nocturnal itching 5
  • Hookworm
  • Strongyloides stercoralis
  • Tapeworms 5
• Sexually transmitted infections:
  • Condylomata acuminata (genital warts)
  • Herpes simplex
  • Syphilis 2

Dermatological Conditions

• Contact dermatitis: From soaps, detergents, toilet paper, wipes (18 of 40 patients in one study had positive patch tests) 6
• Psoriasis: Can affect the perianal region
• Lichen sclerosus: Causes whitish, thinned skin
• Seborrheic dermatitis: Can extend to perianal area 4

Systemic Diseases

• Diabetes mellitus: Causes increased susceptibility to fungal infections
• Liver disease: Cholestatic conditions causing bile acid accumulation 5
• Renal disease: Uremic pruritus in advanced renal insufficiency 5
• Hematological disorders: Iron deficiency can cause generalized pruritus 5
• Malignancy: Both local (anal or colorectal cancer) and systemic malignancies can present with pruritus 4

Medication-Related

• Opioids: Cause pruritus in 2-10% of patients receiving oral administration, 10-50% intravenous, and 20-100% epidural/intrathecal 5
• Antibiotics: Can alter normal flora and predispose to fungal overgrowth
• Steroids: Topical overuse can thin skin and worsen symptoms

Psychological Factors

• Stress and anxiety can exacerbate symptoms and perpetuate the itch-scratch cycle 5

Diagnostic Approach

The Washington classification is commonly used to categorize anal pruritus based on perianal skin abnormalities 4. A thorough evaluation should include:

1. Visual inspection of the perianal area
2. Digital rectal examination to assess for masses or internal hemorrhoids
3. Anoscopy to exclude anorectal diseases or suspicious masses
4. "Sellotape test" for pinworm diagnosis (placing adhesive tape on perianal skin in the morning and examining for ova) 5
5. Blood tests for systemic causes (CBC, ferritin, liver and renal function) when appropriate 5

Clinical Pearls

• Pruritus ani affects up to 5% of the population 7
• Many patients have multiple contributing factors rather than a single cause
• In one study of patients with persistent pruritus ani, 34 of 40 patients had a recognizable dermatosis as the underlying cause 6
• Patients often delay seeking medical attention due to embarrassment 4
• The itch-scratch cycle can perpetuate and worsen symptoms regardless of the initial cause

Understanding the diverse causes of anal itching is essential for effective management and improving patients' quality of life, as this condition can significantly impact mental health and daily functioning.