Benzocaine

Benzocaine is a local anesthetic contained in many topical products, particularly used in the treatment of:
- stasis ulcers and dermatitis,
- otitis externa,
- wounds,
- haemorrhoids and anogenital pruritus,
- sunscreens containing PABA
About 25% of benzocaine-sensitive patients are sensitive to paraphenylendiamine and to sunscreens containing glyceryl para-aminobenzoic acid. Moreover, benzocaine shows cross-reactivity also with aniline dyes, procaine and sulfonamide.


How to determine the relevance of positive patch test reactions to Benzocaine
Relevance is certain or probable if:
- the dermatitis has a typical localization (involvement of skin sites previously treated with topical products containing benzocaine, e.g. anogenital region, external ear duct, perilesional skin of ulcers, stasis dermatitis) is present;
- the dermatitis has an atypical localization (involvement of other skin sites), but exposure to benzocaine containing products is certain or probable;
- the dermatitis is localized to areas exposed to cross-reacting substances and exposure to cross-reacting substances is certain or probable.
Relevance is possible if:
- the dermatitis has an atypical localization and exposure to benzocaine containing products is uncertain or unknown.
Relevance is negative if:
- the dermatitis has an atypical localization and there is no exposure to benzocaine containing products.

In cases where the relevance is possible, or in cases of suspected occupational dermatitis, or for study purposes, it is advisable to perform patch tests with suspected materials or look for benzocaine in products usually not containing benzocaine (safety data sheets, information from manufacturer, analytical investigation)



Paraphenylendiamine (PPDA)
PPD and its derivatives are employed as antioxidants and dyes. PPD is utilised in rubber, leather, industrial oils, photographic work, lithographing, hair dyes
PPD shows cross-reactivity with:
- Azo and aniline dyes,
- para-aminosalicylic acid,
- para-aminobenzoic acid,
- local anesthetics (Benzocaine, Procaine),
- Sulfonamide
- other hair dyes
- isopropyl n-phenyl PPD
- diaminodiphenylmethane.


How to determine the relevance of positive patch test reactions to PPD
Relevance is certain or probable if:
- a dermatitis with the typical pattern of the PPD dermatitis (involvement of face, eyelids, scalp, with edema, erythema and vesicles) is present;
- the dermatitis has an atypical pattern (involvement of other skin sites), but exposure to PPD containing products is certain or probable;
- the dermatitis is localized to areas exposed to cross-reacting substances and exposure to cross-reacting substances is certain or probable.
Relevance is possible if:
- the dermatitis has an atypical pattern (involvement of other skin sites), and exposure to PPD containing products is uncertain or unknown.
Relevance is negative if:
- the dermatitis has an atypical pattern (involvement of other skin sites), and there is no exposure to PPD containing products.

In cases where the relevance is possible, or in cases of suspected occupational dermatitis, or for study purposes, it is advisable to perform patch tests with suspected materials or look for PPD in products usually not containing PPD (safety data sheets, information from manufacturer, analytical chemical investigation)