In this blog we will concentrate on the role of physical contact with chemicals and the effect on psoriasis. For Oral Drug Induced Psoriasis please refer to out blog “PSORIASIS – the Relationship with Drugs”


Various studies have suggested that hypersensitivity to contact  allergens, namely chemicals, in psoriasis is an important and often underestimated, provocative/exacerbating factor in the manifestation and the course of psoriasis.

Dollarphotoclub_80345209 Chemicals

Recently research has focused on allergic contact dermatitis in psoriasis and results have supported the role of contact allergy in provoking psoriatic lesions on palms and soles. Studies of incidence of contact allergy in patients with palmar and plantar psoriasis report the following results:-

  • Positive patch-tests were found in 39.5% of the psoriatic cases with palmo-plantar involvement therefore indicating a significantly greater hypersensitivity to contact allergen in the group of patients with palmo-plantar psoriatic lesions. Some of the allergens that elicited as positive response were – nickel sulphate, epoxy resin, cobalt chloride, phenylenediamine, paraben mix, detergents, potassium dichromate, nickel sulphate, soap for hands, thiuram mix, neomycin sulfat and nickel.1                                                                                                                                                                                                                                                                              
  • In another study in patients with various presentations of psoriasis vulgaris, the researchers concluded that the result of 68% of patients with a positive patch-test, points to delayed type hypersensitivity to contact allergens as a possibly relevant factor in the presentation or course of psoriasis. The most common allergens were tars, nickel sulphate, perfume and balsam of Peru.2.3                                                                                                                                                                                      
  • In another study, the researchers found 19 patients (25%) with different forms of psoriasis (inverse psoriasis, palmoplantar psoriasis, chronic plaque psoriasis, guttate psoriasis and pustular psoriasis) who had positive patch tests. The most common positive patch-tests were to nickel, fragrance mix, coal tar, colophony and neomycin.4                                                                                                                                                                                                                                                                                 
  • Another study reported allergic disease in 21% of patients tested, but a positive RAST test was obtained in 44%. In chronic plaque-type psoriasis a positive RAST test was significantly more common (58%) than in active psoriasis (22%). Grass pollen and house dust mite were the most prevalent sensitizing allergens, with frequencies of 64% and 53%, respectively in the sensitized subjects. Sensitization increased with age and polysensitization was common. Contact dermatitis was verified with patch tests in 12 men and 20 women, of whom 10 had chronic plaque-type psoriasis and 22 active psoriasis. Tar, nickel sulphate, corticosteroid mixture and thiomersal were the most common allergens. No irritant reactions were seen at the concentrations used.5                             

In some of the studies it was found that when the patients with positive patch-tests avoided the topical products containing the incriminated allergens, they showed improvement in their psoriasis. This strongly suggests that hypersensitivity to contact allergens in psoriasis is a relevant provocative/perpetuating factor in manifestations and the course of psoriasis.1

Other research has suggested that there is a possible interaction between the clinical evolution of psoriasis and the production of the cytokines that intervene in immunoreactions involved in cell-mediated responses and in atopy. The Th1 lymphocytes involved in cell-mediated responses seem to act during the active phase of psoriasis, whereas the Th2 lymphocytes active in atopy are active during the non-active plaque-type phase and, for this reason, are more associated with IgE-mediated allergies. In clinical practice, patients with chronic psoriasis are more likely to develop IgE-mediated diseases, whereas in the active phase they will be more affected by contact dermatitis: the greater application of topical treatments during this phase increases the risk of contact dermatitis.5

Researchers concluded that:-

  • Allergic contact dermatitis has a great role in the provoking and maintenance of the psoriasis lesions.
  • Patch-tests should be included as a routine diagnostic procedure in psoriasis, especially in palmo-plantar psoriasis, in long standing psoriasis and in psoriasis resistant to therapy.
  • Avoidance/elimination of selective previously identified materials/antigens with positive patch-test responses may alleviate and make the treatment of chronic, recalcitrant psoriasis more effective.1

The theory proposed for the most likely cause is thought to be due to skin injury caused by exposure to the chemical/material/antigen and the subsequent initiation of the Koebner effect.

See our blog “Koebner Phenomenon”, blog “Psoriasis and Chemical Exposure to Pollution”, “Psoriasis and Smoking” and “Psoriasis and Alcohol Intake”


  1. Heule F. et al.; Delayed-type hypersensitivity to contact allergens in psoriasis; Contact Dermatitis; Volume 38,Issue 2, pages 78–82, February 1998
  2. Heule F, Tahapary GJM, Belloc R, Van Joost Th. Delayed-type hypersensitivity to contact allergens in psoriasis: A clinical evaluation. Contact Dermatitis 1998; 38: 78 -82
  3. Binden A. D., Muston H., Beck M. H. (1994): Intolerance and contact allergy to tar and dithranol in psoriasis. Contact Dermatitis. 31: 185–186.
  4. Fleming C. J., Burden A. D. (1997): Contact allergy in psoriasis. Contact Dermatitis. 36: 274–276.
  5. Pigatto P.D.; Atopy and Contact Sensitization in Psoriasis; Acta Derm Venereol 2000; Suppl 211: 19-20
  6. Thappa DM. The isomorphic phenomenon of Koebner. Indian J Dermatol Venereol Leprol 2004;70:187-9