Beyond dermatological conditions, scalp pain and discomfort can arise from a complex interplay of neurological, systemic, psychological factors, and exposure to certain chemicals in personal care products.

Neuropathic conditions involve damage or dysfunction of the nervous system, leading to sensations like itching, burning, tingling, or pain. The scalp is densely innervated by branches of the trigeminal nerve and cervical nerves, and hair follicles themselves contain various nerve endings.

• Scalp Dysesthesia: This is a neuropathic phenomenon characterized by subjective complaints of itching, burning, pain, prickling, and/or trichodynia (hair pain), often without visible skin lesions, though redness may be present. It is considered a somatoform disorder. Triggers can be endogenous (e.g., stress, emotional disturbances) or exogenous (e.g., inappropriate topical products, cosmetics).

  
  

• Trichodynia (Hair Pain): This refers to a painful sensation in the hair, frequently associated with hair loss. Patients describe it as if their hairs are "bent in the wrong way" or like "stitches". It is more common in women and may be linked to perifollicular inflammation, increased substance P in hair follicles, psychiatric disorders, and nutritional deficiencies. Combing, drying, or wearing hair accessories can trigger this pain.

  
  

• Postherpetic Neuralgia (PHN): This can occur after herpes zoster (shingles), particularly in the trigeminal nerve's ophthalmic division (V1), resulting in chronic pain and localized pruritus on the forehead and anterior scalp.

  
  

• Other Neuropathic Causes: Conditions like diabetes mellitus, brain and spinal cord injuries, brain tumors, narrowing of bony foramina from osteoarthritis, and Wallenberg syndrome can also lead to neuropathic scalp pruritus.

  
  

Systemic conditions, which are internal diseases affecting the body, can also manifest as scalp pruritus. Examples include chronic kidney disease, cholestatic liver disease, certain hematologic malignancies, and dermatomyositis. Scalp pruritus in dermatomyositis, for instance, has been associated with small-fiber neuropathy. Drug-induced pruritus (e.g., by dobutamine) and eosinophilic arteritis of the scalp are also reported systemic causes.

Psychogenic factors play a role, as chronic stress or psychiatric disorders such as depression, anxiety, delusional parasitosis, obsessive-compulsive disorders, and tactile hallucinations can cause or exacerbate scalp pruritus. Psychological factors can directly influence the perception of itch. The scalp's easy accessibility often makes it a frequent site for excoriations in these cases.

A common, yet often undiagnosed, condition is sensitive scalp (SSc). Defined as unpleasant sensations (stinging, burning, pain, pruritus, tingling) on the scalp in response to normal stimuli, without overt skin lesions, SSc is a significant issue for many.

• Prevalence: SSc affects a substantial portion of the population, with reported prevalence rates ranging from 32% to 44% in French populations and 56% in Korean women. It is more common in women and its prevalence increases with age.

  
  

• Symptoms and Triggers: Itching is a very common symptom, reported by about 60% of individuals with SSc. SSc can be triggered by a variety of environmental factors (heat, cold, pollution, dry or wet air, water) and personal care practices (shampoos, hair dyeing products). Emotional stress can also act as a trigger.

  
  

• Associations: SSc may be associated with hair loss, seborrheic dermatitis, and atopic dermatitis. Some studies suggest SSc is linked to a disturbed skin barrier, higher pH, increased transepidermal water loss, and elevated sebum production, as well as an altered scalp microbiome (e.g., higher Propionibacterium acnes).

  
  

• Diagnosis and Management: Diagnosis is primarily guided by patient history, as there are no specific laboratory or histological findings. Management focuses on identifying and avoiding triggers, using non-irritating and fragrance-free hair care products, and hydrating the scalp. For severe or refractory cases, topical corticosteroids, calcineurin inhibitors, or even systemic treatments like tricyclic antidepressants, selective serotonin-norepinephrine reuptake inhibitors, and anticonvulsants (e.g., gabapentin, pregabalin) may be considered, especially for trichodynia. Botulinum toxin injections have also been explored for refractory trichodynia.

  
  

Finally, chemical exposures from personal care products can directly induce or exacerbate scalp pain and discomfort. Many beauty and personal care products contain toxic chemicals, including endocrine disruptors, allergens, and carcinogens, which pose significant health risks.

• Harmful Ingredients: Formaldehyde and formaldehyde-releasing preservatives (FRPs), common in hair straighteners and other products, are known human carcinogens and can cause allergic contact dermatitis. Fragrances in hair products are frequent causes of allergic contact dermatitis and often contain undisclosed chemicals due to regulatory loopholes. Phthalates, found in hair care products, are linked to endocrine disruption, developmental and reproductive toxicity, and cancer.

  
  

• Disparities and Occupational Risks: Hair straighteners are used more frequently by Black women, driven by racialized beauty standards, and have been associated with increased risks of uterine fibroids and earlier age at menarche. Hair salons can be hazardous workplaces due to daily exposure to numerous chemicals, leading to various health issues including dermatitis and other skin conditions for workers. Many chemicals found in U.S. personal care products are banned in Europe, highlighting potential regulatory gaps. Targeted agents that regulate the scalp microbiome, such as controlling the balance between Cutibacterium and Staphylococcus or reducing low-abundant environmental bacteria, may offer future solutions for itch re