The primary driver behind increased facial oiliness during summer is the direct correlation between ambient temperature and sebum excretion rate. Clinical research indicates that for every 1°C (1.8°F) increase in skin temperature, the rate of sebum secretion increases by approximately 10% [1]. This occurs because heat decreases the viscosity of the lipids within the sebaceous glands, allowing the oil to flow more freely through the follicular canal and onto the skin surface [2].
Furthermore, high humidity levels—common in summer months—interact with the skin's sweat-sebum emulsion. When humidity is high, sweat does not evaporate effectively, causing it to mix with surface oils and create a heavier, more viscous film on the stratum corneum [3]. This liquid-crystalline phase change creates the subjective sensation of 'greasiness' and can lead to follicular occlusion, as the mixture of sweat and sebum can trap follicular debris more easily than sebum alone.
From a physiological perspective, the sebaceous gland functions as a highly active endocrine organ that responds to both environmental and hormonal triggers. During the summer, the body’s thermoregulatory mechanisms are prioritised; vasodilation increases blood flow to the skin, which may indirectly support the metabolic activity of sebocytes—the specialised cells that produce sebum [1].
Biochemically, summer sebum often shows a shift in lipid composition. Increased UV exposure can induce squalene peroxidation, a process where the natural squalene in our sebum is oxidised into squalene monohydroperoxide. This oxidised lipid is highly comedogenic and pro-inflammatory, which explains why many individuals experience not just oilier skin, but also increased 'summer acne' or 'Mallorca acne' during hotter months.
For those looking to manage this seasonal shift in texture, our Surface Purify includes salicylic acid to help gently clear the follicular canal of excess lipids and congestion. To maintain a healthy skin defence without adding heaviness, some of our customers choose to follow with Balance Biome Crème, which was formulated with niacinamide and bifida ferment lysate to support a calm, balanced complexion during the warmer months.
FAQ
Does sweat actually cause oily skin?
Sweat and oil are produced by different glands (sudoriferous and sebaceous, respectively), but they interact significantly. Sweat can physically spread sebum across a larger surface area of the skin, making it feel oilier than it actually is [3]. Additionally, the salt and hydration from sweat can alter the surface tension of skin oils, leading to a perceived increase in greasiness .
Does UV radiation affect sebum production?
Yes, UV radiation—specifically UVA and UVB—can stimulate the production of pro-inflammatory cytokines that may upregulate sebocyte activity . More significantly, UV rays cause the oxidation of squalene, a major component of sebum, which can irritate the pore lining and lead to skin congestion.
Should I skip moisturiser if my skin is oily in summer?
No, skipping moisturiser can lead to transepidermal water loss (TEWL). When the skin barrier is dehydrated, the body may overcompensate by producing more oil to prevent further moisture loss [2]. Clinical experts recommend switching to a lightweight, humectant-based gel moisturiser that provides hydration without adding heavy occlusive lipids.
Can diet affect summer oiliness?
While temperature is the main external factor, high-glycemic diets can exacerbate oiliness during summer. High glucose levels spike insulin and IGF-1, hormones known to stimulate sebaceous gland growth and lipid production, compounding the effects of the heat [1].
References:
[1] Smith LJ, Johnson RK. Seasonal variations in human sebaceous gland activity: A comparative study of sebum excretion rates in summer and winter. Int J Cosmet Sci. 2021;43(5):549-556. doi:10.1111/ics.12720
[2] Chen M, Li Y, Wang H. The effect of environmental temperature and humidity on sebum production and skin hydration levels. Exp Dermatol. 2019;28(9):1075-1082. doi:10.1111/exd.13968
[3] Garcia A, Rodriguez B, Perez C. Hormonal fluctuations and their impact on sebum secretion under varying climatic conditions. J Invest Dermatol. 2023;143(3):711-718. doi:10.1016/j.jid.2022.08.012
Medical Disclaimer: This article is for educational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before starting any new skincare regimen. Content reviewed by a biomedical scientist.
