Paresthesia (Formication): Causes of Crawling Sensations and When to Seek Care

Formication—the sensation of insects crawling on or under the skin—is a type of paresthesia. It is a neurological symptom, not evidence of actual infestation.

Common Causes

• Peripheral neuropathy: Diabetes (most common), B12 deficiency, alcohol, chemo, idiopathic.
• Nerve compression/radiculopathy: Cervical (C5–C8 → arm/hand), lumbar (L5/S1 → leg/foot), carpal/cubital tunnel.
• Medication side effects: Stimulants, SSRIs/SNRIs (initiation/withdrawal), anticonvulsants, opioids.
• Substance use/withdrawal: Cocaine, methamphetamine, alcohol withdrawal, benzodiazepine withdrawal.
• Systemic diseases: Thyroid (hypo/hyper), renal/hepatic failure, autoimmune (Sjögren's, SLE), Lyme, HIV.
• Psychiatric: Delusional parasitosis (fixed false belief of infestation), anxiety, psychosis.
• Cutaneous: Dry skin (xerosis), eczema, scabies (actual mites – burrows visible), contact dermatitis.

Diagnostic Approach

1. History: distribution, timing, triggers, medications, substances, psych history.
2. Exam: skin (burrows, excoriations), neuro (sensory, reflexes, strength), cranial nerves.
3. Labs: CBC, CMP, TSH, B12/folate, HbA1c, ESR/CRP, HIV, RPR, vitamin D.
4. Nerve conduction studies / EMG if neuropathy/radiculopathy suspected.
5. Skin scraping if scabies possible.

Treatment

• Treat underlying cause (glucose control, B12 replacement, medication adjustment, thyroid normalization).
• Symptomatic: gabapentin, pregabalin, duloxetine, topical capsaicin/lidocaine.
• Delusional parasitosis: antipsychotics (pimozide, risperidone) + psychotherapy; avoid validating delusion.
• Scabies: permethrin 5% cream / ivermectin.

When to Seek Care Urgently

• Progressive weakness, numbness, bowel/bladder changes (cauda equina).
• New cranial nerve deficits.
• Signs of stroke (FAST).
• Severe psychiatric distress.

Do not self-treat with pesticides or excessive cleaning. See a neurologist or dermatologist for proper evaluation.