What causes itchiness?

Causes of Itchiness

Itchiness (pruritus) is caused by multiple underlying conditions including dermatological disorders, systemic diseases, neurological conditions, psychological factors, and medication reactions. 1

Dermatological Causes

Primary Skin Disorders

• Eczema/atopic dermatitis: Characterized by chronic pruritus typically starting in childhood with erythema, xerotic scaling, lichenification, and hyperpigmentation 1
• Seborrheic dermatitis: Presents with greasy yellowish scaling and itching, particularly affecting the ears, scalp, and central face 1
• Contact dermatitis:
  • Irritant contact dermatitis: Direct chemical damage causing inflammation
  • Allergic contact dermatitis: Reaction to allergens like metals (nickel), chemicals, plastics, rubber, or drugs 1
• Urticaria: Presents with wheals and intense itching, often triggered by infections, medications, foods, or physical stimuli 2
• Psoriasis: Characterized by well-demarcated plaques with silvery scale 1
• Xerosis cutis (dry skin): Common cofactor contributing to chronic itch, especially in elderly patients 3

Systemic Causes

Hematological Disorders

• Iron deficiency: Can cause generalized pruritus without rash, responding to iron replacement 1
• Iron overload: Associated with generalized pruritus in haemochromatosis 1
• Polycythemia vera: Characterized by aquagenic pruritus (itching triggered by water contact) 1
• Lymphoma: Particularly Hodgkin lymphoma, presenting with itching, weight loss, fevers, and night sweats 1

Renal Disease

• Uremic pruritus: Common in end-stage renal disease or chronic kidney disease, affecting 42% of patients on hemodialysis 1
• Characteristics: Can be generalized or localized to the back, face, or arteriovenous fistula arm 1

Hepatic Disease

• Cholestatic liver disease: Associated with generalized pruritus 1

Endocrine Disorders

• Thyroid dysfunction: Both hyperthyroidism and hypothyroidism can be associated with pruritus, though evidence is limited 1
• Diabetes mellitus: Can cause regional pruritus affecting the trunk due to diabetic neuropathy 1

Neurological Causes

• Neuropathic pruritus: Caused by pathology along the afferent pathway of the nervous system 4
  • Postherpetic neuropathy
  • Brachioradial pruritus
  • Notalgia paraesthetica
  • Small fiber neuropathy (in conditions like diabetes, Guillain-Barré syndrome, sarcoidosis) 1
• Central nervous system disorders: Spinal cord tumors, multiple sclerosis, brain lesions 4

Psychological and Emotional Factors

• Stress and emotional triggers: Negative emotions like stress, fear, rage, and embarrassment can trigger or worsen pruritus 1
• Psychiatric disorders: Depression, anxiety, obsessive-compulsive disorder 1
• Functional itch disorder: Diagnosed when three compulsory criteria are met (chronic pruritus >6 weeks, no somatic cause, variations in intensity with stress) plus three of seven optional criteria 1

Medication-Related Causes

• Drug reactions: Various medications can cause pruritus as an adverse effect 1
• Opioids: Can produce itch through central and peripheral mechanisms 5

Diagnostic Approach

Initial Laboratory Workup

• Complete blood count with differential: To evaluate for iron deficiency, polycythemia, lymphoma 6
• Ferritin levels: To assess iron status 1
• Renal function tests: To identify kidney disease 6
• Liver function tests: To detect hepatic disorders 6
• Thyroid function tests: If clinical features suggest thyroid disease 1, 6
• Blood glucose: To screen for diabetes 6

Special Considerations

• Elderly patients: Higher risk for systemic causes of pruritus 3
• Patients >60 years with diffuse itch <12 months: Increased concern for underlying malignancy, especially with history of liver disease 6
• Unexplained iron deficiency: Consider testing for tissue transglutaminase antibodies to rule out celiac disease 1

Management Principles

General Measures

• Identify and treat underlying cause when possible
• Avoid aggravating factors: NSAIDs, alcohol, overheating, stress 2
• Topical treatments:
  • Emollients for dry skin 1
  • Cooling antipruritic lotions (calamine, 1% menthol in aqueous cream) 2
  • Topical corticosteroids for inflammatory conditions 7

Specific Treatments

• Antihistamines: Non-sedating H1 antihistamines as first-line therapy for many causes of pruritus 2
• Topical anti-inflammatory agents: For dermatitis and other inflammatory skin conditions 1
• Targeted therapy: Based on underlying cause (e.g., iron replacement for iron deficiency, adequate dialysis for uremic pruritus) 1

By identifying the underlying cause of pruritus and implementing appropriate treatment strategies, most patients can achieve significant relief from this distressing symptom.