The primary difference between physical (mineral) and chemical sunscreens lies in their active ingredients and their primary mechanisms of action. Physical sunscreens utilise inorganic minerals, specifically Zinc Oxide and Titanium Dioxide, which act as a physical barrier on the skin's surface. These minerals primarily reflect and scatter ultraviolet (UV) radiation away from the skin, though modern micronised formulations also absorb a significant portion of UV rays [1]. They provide broad-spectrum protection against both UVA and UVB rays immediately upon application, making them a popular choice for those with sensitive skin or inflammatory conditions like melasma [2].
Chemical sunscreens, conversely, employ organic (carbon-based) compounds such as oxybenzone, avobenzone, octisalate, and octocrylene. Rather than sitting on top of the skin, these filters are absorbed into the stratum corneum where they undergo a chemical reaction. They function by absorbing UV radiation and converting it into a small amount of negligible heat, which is then dissipated from the skin [3]. Unlike mineral filters, chemical sunscreens often require approximately 20 minutes to 'set' and become fully effective, but they generally offer a more cosmetically elegant, sheer finish that is easier to spread and leaves no white cast, which many users find to be the best option for daily wear under makeup [4].
From a formulation science perspective, the 'best' sunscreen is the one that an individual will wear consistently and correctly. In Australia, where UV indices are consistently high, the efficacy of both types is strictly regulated by the Therapeutic Goods Administration (TGA). While physical filters are traditionally described as reflectors, research indicates that Zinc Oxide actually absorbs about 95% of UV radiation, with only 5% being reflected [1]. The distinction is therefore more about the chemical structure of the filter rather than a total divergence in physical behaviour.
Photostability is a critical factor in the performance of these products. Many older chemical filters, particularly avobenzone, were prone to degradation under UV exposure, requiring stabilisers like octocrylene to maintain efficacy [5]. In contrast, mineral filters are inherently photostable, meaning they do not break down over time when exposed to the sun. However, the move toward 'nano' sized mineral particles has improved the aesthetics of physical sunscreens, minimising the traditional chalky residue while maintaining high-level photoprotection [6].
While choosing your preferred UV defence, you might also consider how your daily moisturiser supports the skin's natural resilience against environmental stressors. For those seeking a calm, balanced complexion alongside their sun protection, our Balance Biome Crème is formulated with Bifida Ferment Lysate and Niacinamide to help maintain a healthy microbiome and strengthen the skin's moisture barrier.
FAQ
Which is best for sensitive or acne-prone skin?
Physical sunscreens are generally considered best for sensitive skin or those prone to eczema and rosacea, as mineral filters are not absorbed into the skin and are less likely to cause allergic contact dermatitis [2]. Zinc oxide also possesses mild anti-inflammatory properties. For acne-prone skin, mineral options are often preferred, though it is crucial to ensure the overall formulation is labelled 'non-comedogenic' to avoid clogging pores [7].
Can you mix mineral and chemical sunscreens together?
It is not recommended to mix different sunscreen products manually as this can destabilise the formulation and create 'gaps' in the protective film on the skin [5]. However, many modern Australian sunscreens are 'hybrid' formulations, containing both mineral and chemical filters. These are often the best performing products as they combine the immediate protection and stability of minerals with the sheer, lightweight texture of chemical filters [4].
Does the 'white cast' affect the SPF rating?
The 'white cast' associated with mineral sunscreens is caused by the large particle size of the minerals reflecting visible light. While it doesn't negatively impact the SPF, it often leads to under-application by the user to avoid the aesthetic effect. Since SPF is dose-dependent, under-applying significantly reduces the actual protection received. Micronised or tinted mineral sunscreens are the best solution to ensure adequate application without the ghostly appearance [6].
References:
[1] Cole C, et al. Metal oxide sunscreens: Protectants, photo-catalysts, or both? Photodermatol Photoimmunol Photomed. 2016;32(1):5-10. doi:10.1111/phpp.12214
[2] Schneider J, et al. The efficacy and safety of sunscreen use for the prevention of skin cancer. Australian Prescriber. 2019;42(2):56-59. doi:10.18773/austprescr.2019.015
[3] Latha MS, et al. Sunscreening Agents: A Review. J Clin Aesthet Dermatol. 2013;6(1):16-26.
[4] Geoffrey K, et al. Sunscreen products: Rationale for use, formulation development and regulatory considerations. Saudi Pharm J. 2019;27(7):1009-1018. doi:10.1016/j.jsps.2019.08.003
[5] Kockler J, et al. Photostability of sunscreens. J Photochem Photobiol B. 2012;107:1-10. doi:10.1016/j.jphotobiol.2011.12.007
[6] Smijs TG, et al. Titanium dioxide and zinc oxide nanoparticles in sunscreens: focus on their safety and effectiveness. Nanotechnol Sci Appl. 2011;4:95-112. doi:10.2147/NSA.S18419
[7] Draelos ZD. Sunscreens and cosmetics. Clinics in Dermatology. 2001;19(4):424-430. doi:10.1016/S0738-081X(01)00193-4
