The rationale for the use of vitamin D derivatives in the treatment of psoriasis is based on the observation that patients with hypocalcemia often develop various forms of psoriasis, most notably the pustular form. In one case, a patient who had undergone thyroidectomy developed repeated flares of pustular psoriasis after decreases were made in her dosage of ergocalciferol (Vitamin D 2 ); each episode was related to severe hypocalcemia and resolved after her serum calcium levels normalized. 14 Another patient with osteoporosis experienced dramatic improvement in severe psoriasis after receiving an oral form of vitamin D. 15 This finding, along with the discovery that the bioactive form of 1,25-dihydroxycholecalciferol has been shown to inhibit keratinocyte proliferation and promote keratinocyte differentiation, 16 has led to the development of vitamin D analogs for the treatment of psoriasis.
You can buy some topical corticosteroids "over-the-counter" without a prescription. For example, for dermatitis, you can buy the steroid cream called hydrocortisone 1% from your pharmacy. Do not apply this to your face unless your doctor has told you to do so. This is because it may trigger a skin condition affecting the face ( acne or rosacea. ) Long-term use may also damage the skin. On your face this would be more noticeable than the rest of your body. So usually only weak steroids are used on the face. Those which are suitable are prescription-only.
Transdermal patches can be a very precise time released method of delivering a drug. Cutting a patch in half might affect the dose delivered. The release of the active component from a transdermal delivery system (patch) may be controlled by diffusion through the adhesive which covers the whole patch, by diffusion through a membrane which may only have adhesive on the patch rim or drug release may be controlled by release from a polymer matrix. Cutting a patch might cause rapid dehydration of the base of the medicine and affect the rate of diffusion.