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SUMMARY
Scalp contact dermatitis (SCD) is an inflammatory disorder of the scalp triggered by the application of one or more allergenic substances able to evoke either an irritant or immune response.
The burden of SCD is increasing worldwide due to the growing trend of performing cosmetic procedures on the scalp, which includes hair dyes, bleaches, extensions, wigs, perming, and straightening.
Keratin treatments are a common cause of scalp dermatitis.
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TIPS FOR DIAGNOSIS
The signs of SCD often extend to surrounding or distant anatomical areas, where the clinical signs often appear more pronounced than on the scalp.
Itching and burning are almost constant symptoms of SCD and should always trigger suspicion of possible sensitization.
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TIPS FOR TREATMENT
Treatment of acute SCD consists of topical or systemic corticosteroids according to the severity of the delayed-type reaction.
Immediate-type reactions, including contact urticaria, benefit from antihistamine therapy and systemic steroids.
Long-term treatment relies on allergen avoidance.
Dupilumab can be considered in severe cases.
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DON’T FORGET
Delayed-type reactions always require a primary sensitization. This event may occur after exposure to the same allergen coming from a different source than the offending one; however, can also be secondary to long-term use of any topical product.
Always assess the clinical relevance of positive patch tests and consider allergen cross-reactivity.
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PITFALLS AND CAUTIONS
The latency between a SCD and the initial use of a scalp product could last a long time.
Topical minoxidil causes much more frequently skin irritation than a skin allergy.
Individuals with atopic diathesis are at increased risk of developing immediate-type reactions to allergens, including contact urticaria or respiratory symptoms.
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EXPERT PEARLS
Shampoos are a very uncommon cause of contact dermatitis as they are diluted and contact with the skin is short.
A mild to severe hair loss may begin 2 to 4 months after the episode of SCD.
Aggravation of androgenetic alopecia is a possible complication of SCD.
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PATIENT EDUCATION POINTS
Do not overlook scalp symptoms or treatment failure and aggravation of the underlying scalp disorders; these can be key signs of an allergic reaction to the applied products.
In the case of a suspected or confirmed allergy to metals, pay maximum attention to the use of hair accessories, hairpins, glasses, and jewelry in nearby body areas.
Para-phenylenediamine (PPD) is the most common allergen responsible for SCD due to hair dyes.
Allergic hair dye patients willing to use a new dye should have a “repeated open application test” and wait at least 48 hours for a possible allergic reaction.
Alternative hair dyes for sensitized patients include botanical dyes, such as Henna, Cassia, and Indigo, and some PPD derivatives with a lower skin sensitization potential than PPD, such as para-toluenediamine sulfate, 4-amino-2-hydroxytoluene, and 2-methoxymethyl-p-phenylenediamine.
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SCD represents an important inflammatory disease that mainly afflicts women over the age of 40. ...