Summary: A new study suggests that patients in sunnier climates may require higher doses of Botox for effective cosmetic treatment of facial lines due to increased muscle activity and environmental factors.

Key Takeaways:

  1. Higher Botox Dosage Required in Sunnier Climates: The study indicates that individuals in “high-sun” environments, like Malta, may need more Botox to achieve similar levels of muscle paralysis compared to those in less sunny settings, such as London, due to increased muscle activation from squinting and possibly higher temperatures.
  2. Adjustments to Treatment Protocols: Plastic surgeons may need to modify their standard Botox dosing protocols to consider the climatic conditions of their practice locations to ensure effective and consistent cosmetic results.
  3. Implications for Training and Treatment Costs: Although the differences in dosage requirements are small, they are significant enough to suggest that standardized treatment protocols may lead to under-treatment in sunnier climates, affecting both the training of practitioners and the predictability of treatment outcomes.


Patients living in “high-sun” climates may require higher doses of Botox to achieve good results in the cosmetic treatment of facial lines and wrinkles, reports a study in the July issue of Plastic and Reconstructive Surgery, the official medical journal of the American Society of Plastic Surgeons (ASPS).

“In countries with higher sun exposure, higher doses of Botox may be needed to achieve the same degree of forehead muscle paralysis, compared to less-sunny countries,” comments lead author Kim L. Borsky, MBBS, MD, MRCS, of the U.K.-based Stoke Mandeville Hospital. “Our results suggest that plastic surgeons may need to adjust their Botox dosing protocols to account for the effects of climate on the results of this cosmetic treatment.”

Could Sun Exposure Affect Responses to Cosmetic Botox?

Administration of “injectables” is the most common minimally invasive cosmetic procedure performed by plastic surgeons. According to ASPS statistics, injection of neuromodulators such as botulinum toxin type A—best known by the brand name Botox—was performed more than 8.7 million times in 2022. Botox blocks nerve signals to the injected muscles, causing reversible muscle paralysis. This allows softening and relaxation of lines and wrinkles of the overlying skin.

Plastic surgeons have noticed variations in the improvement achieved by Botox injections. While several factors are known to affect the response – including muscle mass, gender, age, and ethnicity—other unidentified factors may also play a role.

Could climate contribute to differences in the response to cosmetic Botox injections? Borsky and her colleagues compared outcomes of Botox treatment in two groups of patients: a “high-sun” group of 292 women in the Mediterranean island nation of Malta and a “low-sun” group of 231 women treated in London. Patients in Malta were treated during the summer months, while the UK patients were treated in the winter months.

Botox Treatments ‘May Need to Account for Climate’

The patients underwent Botox injections into the glabellar muscles of the lower forehead; all treatments were performed by experienced plastic surgeons following a standardized technique. At follow-up visits, patients received “top-up” doses as needed to achieve “full clinical paralysis.” The total Botox dose needed to achieve this result was compared between the high-sun and low-sun groups.

The results showed a higher average total Botox dose in the high-sun group: 29.2 versus 27.3 units. Patients in Malta also received a higher average top-up dose: 2.24 versus 1.98 units. The differences in Botox dose remained significant after adjustment for age and other factors.

Why would patients in sunny climates need more Botox? Noting that the glabellar muscles are the main muscle group involved in squinting, Borsky and colleagues speculate that the difference may reflect greater development and functional activation of these muscles. Other possibilities include the effects of higher temperatures or the direct effects of sunlight on the response to Botox.

The researchers note that the small difference in their study isn’t likely to have a large impact on treatment costs, but it may have implications for training and treatment. “Rigid protocols about doses and distributions may lead to undertreatment if applied in sunnier climates,” Borsky and her coauthors conclude. “Treatment protocols may need to account for the climate in which treatments are being undertaken to achieve more predictable results.”