A formula that performs well in a heated London office in January will perform differently on a warm July evening. Temperature and humidity are not background conditions — they are active variables that change the evaporation rate, the projection radius, and the act structure of the same formula. This is why seasonal fragrance selection is not a marketing affectation. It is a performance decision.
Temperature increases the evaporation rate of all aromatic compounds. A warm environment — warm ambient air, warm skin from sun exposure or physical activity — accelerates the departure of every tier of the formula simultaneously. Act 1 evaporates faster, projecting more intensely and departing more quickly. Act 2 compresses. Act 3 arrives earlier but may also depart faster than it would in cooler conditions. The total longevity can decrease in very high temperatures even though the formula seems more present in the first hour. Humidity has a different effect: high ambient humidity slows the evaporation of aromatic compounds by reducing the concentration gradient between the skin surface and the surrounding air — the air is already carrying more moisture and aromatic particles, reducing the rate at which new molecules depart the skin. High humidity can extend longevity and sustain the sillage cloud around the wearer. Low humidity and cold, dry air accelerate evaporation and compress the act structure.

THE INSIGHT
The practical implication for formula selection: dense, resinous, warm base-structure formulas — orientals, ambers, oud-heavy accords — are designed for cool-to-cold, dry conditions. Their low volatility compounds produce their correct performance when the ambient temperature and dryness are driving evaporation at a moderate rate. In hot conditions, the same dense formula can become overwhelming — its Act 3 base materials, intended to develop slowly over hours, are driven off the skin more rapidly, producing a heavy, airless impression. Lighter, citrus-forward, high-volatility formulas — fresh, aquatic, light florals — are designed for warm or humid conditions where their fast evaporation rate is appropriate to the ambient conditions and their projection is natural rather than aggressive.
TAKEAWAY

Match formula weight and volatility profile to the thermal conditions of wear. In winter in London — cool, often dry, low ambient temperature — a resinous, warm base structure performs correctly. In summer or in warm indoor environments — a lighter formula with a fresh or floral structure projects appropriately. This is not about seasonal trends. It is about matching the formula's evaporation physics to the thermal environment in which it will be worn.