30% mannitol cream has shown its ability to reduce the activation of the Capsaicin (TRPV1) (Transient Receptor Potential Vanilloid 1) receptor, a likely cause of the pain of post-herpetic neuralgia (PHN). This randomized placebo-controlled crossover study compares PHN pain one week before, for one week on the randomly assigned mannitol versus placebo cream and, after a three day washout, for one week on the other cream. Following this crossover study, participants receive mannitol cream for three months. Pain levels will be checked to assess whether continued use of this cream significantly reduces the pain levels associated with PHN. If pain persists beyond 3 months, participants will be offered mannitol and menthol cream for one month following which their pain levels will be checked.

Pain levels: 0 to 10 Numerical Rating Scale (NRS), medication and alcohol intake will be checked daily for one week prior to randomization in 20 participants with post herpetic neuralgia, lasting more than three months. Following this 10 will be randomized to apply 30% mannitol in vehicle cream and 10 to apply vehicle cream alone for one week during which daily pain levels and use of medication and alcohol will be measured together with the mode of application (rubbing in or applying it to cling wrap then applying the cream coated cling wrap to the skin in cases of severe allodynia). After a three day washout period, they will be given the cream they did not receive previously for one week. The same variables will be recorded daily. The data collected in the first 24 days will be used to generate a power analysis. Following this, all subjects will receive the 30% mannitol cream to apply for three months. Their pain levels, medication intake and method of application will be measured once a month for three months. T-tests will compare the pain levels for mannitol and placebo users before and after one week of the use of each cream to see if the mannitol cream provides better short term pain relief than placebo. Repeated measures ANOVA (Analysis Of VAriance) will compare pain levels before using the mannitol cream and monthly for three months to assess the long-term effects of mannitol cream. Variables collected at each visit, which will not be used for statistical purposes in the current very small pilot project but may be used in a later study, include: application method, effect and side effects of the cream, medication and alcohol use, PHQ - 9 (Personal Health Questionnaire, 9 questions), and questions from the brief pain inventory score. At three months, a satisfaction score will be added to the database. If pain persists beyond 3 months, participants will be offered mannitol and menthol cream for one month, following which their pain levels, PHQ - 9 and brief pain inventory scores will be checked.

Inclusion Criteria

1. - Suffering from post-herpetic neuralgia on the trunk or the extremities for at least three months.
2. - Maximum daily pain score greater than or equal to 5/10.
3. - Having failed to improve with at least one neuropathic pain medication.

4- Able and willing to fill a fluid survey NRS pain scale and a medication intake questionnaire daily, preferably online but on paper, if unable, for the first 24 days of the study, then once a month for three months..

5 - Preferably have access to someone who can apply cream to their back if they have pain in the back and cannot reach the area.

6 - If that is not possible, ability to apply the cream to their own back, using an applicator which will be supplied.

Exclusion Criteria:

1. Allergies to any of the ingredients of the cream

2. Open lesions or abrasions on the skin where the cream will be applied

3. Using corticosteroids

4. Unwilling to stop using other topical products (creams or patches) for the treatment of post-herpetic neuralgia

5. Pregnant, breast-feeding or not using birth control

6. Suffering from severe chronic pain from a cause other than post-herpetic neuralgia

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