The purpose of this study is to determine if the new vehicle formulations containing ingenol mebutate are as safe and effective as Picato® gel 0.05% (it's current vehicle formulation) when applied to AK lesions on the forearm for two consecutive days.

This study will be run in 2 parts. The first part involves applying escalating concentrations of the new vehicle formulations containing ingenol mebutate to AKs on the forearms. Reactions and safety will be compared to Picato® (a registered and marketed ingenol mebutate gel) to ascertain if the new vehicle formulations are at least as safe and effective as Picato® . The purpose of part 2 is to select the concentration in the "new formulation" that produces this same, if not better response, as Picato® and with a similar or better safety profile.

Inclusion Criteria:

• Must be male or female and at least 18 years of age.
• Female patients must be of non-childbearing potential or if of childbearing potential then negative serum and urine pregnancy test and using effective contraception.
• Ability to provide informed consent.

Exclusion Criteria:

• location of the selected treatment area within 5cm of an incompletely healed wound or within 5cm of a suspected basal cell carcinoma or squamous cell carcinoma
• undergone Cosmetic or therapeutic procedures within 2cm of the selected treatment area in the 2 weeks prior to the treatment visit
• presence of sunburn within the selected treatment areas
• use of acid-containing therapeutic products within 2cm of the selected treatment area in the 2 weeks prior to the treatment visit
• previous enrolment in this clinical trial
• prior treatment with ingenol mebutate on the forearms
• use of topical moisturisers/creams/lotions, artificial tanners or topical steroids within 2cm of the selected treatment areas in the 2 weeks prior to the treatment visit
• treatment with immunomodulators, or interferon/interferon inducers or systemic medications that suppress the immune system within 4 weeks of the treatment visit
• treatment with 5-FU, imiquimod, diclofenac,or photodynamic therapy within 2 cm of the treatment area in the 8 weeks prior to the treatment visit
• use of systemic retinoids
• those who are currently participating in any other clinical trial
• females who are pregnant or are breastfeeding
• those known or suspected or not being able to comply with the requirements of the protocol or provide consent