丙二醇（PG）与植物甘油（VG）均被归类为 humectants——具有强烈吸水性的物质。这一特性被称为 hygroscopicity, is key to their function in e-liquids, as they effectively "pull" water molecules from the surrounding air and condense them into a visible, inhaled aerosol.
Propylene Glycol (PG):PG is significantly more hygroscopic than VG. When the aerosol is inhaled, the PG molecules immediately seek equilibrium by drawing moisture from the nearest available source: the mucous membranes of the mouth, throat, and respiratory tract. This localized, temporary dehydration is the primary mechanism behind the common "dry mouth" or "cottonmouth" sensation experienced by many vapers. A higher PG-to-VG ratio dramatically exacerbates this effect.
Vegetable Glycerin (VG):While also hygroscopic, VG is larger and less volatile than PG, resulting in a slightly less aggressive moisture-pulling effect. Its higher viscosity tends to produce a smoother, denser vapor (often called "clouds") which is often perceived as less harsh.
PG is also the principal component responsible for delivering the traditional, satisfying "throat hit" sensation, independent of nicotine. Its lower viscosity and greater volatility allow it to be more readily atomized and carried deeper into the airways. Furthermore, it is a superior solvent for flavor compounds compared to VG, meaning a high-PG blend will present flavor and irritation molecules more effectively to the throat's sensory receptors. A higher PG concentration inherently intensifies the delivery 任何刺激性风味分子的。
The Organic Acid Culprits: Why "Sour" Means "Harsh"
在某些水果风味中，最关键的化学因素在于喉感的差异，主要取决于其所含的 organic acids used to achieve a realistic "sour" or "tart" profile. These acids are naturally occurring in fruits and are essential to capturing profiles like green apple, citrus, berries, and especially sour candies.
1. 苹果酸：最主要的刺激物
Malic Acid is the organic acid most frequently responsible for the sharp, tartness associated with fruits like apples, cherries, and sour candies. In flavor formulation, it is used to give a distinct "pucker" effect.
Mechanism of Irritation:苹果酸，一种二羧酸，可能成为 respiratory irritant when vaporized and inhaled. It is moderately acidic and, when deposited onto the sensitive epithelial lining of the throat, it acts as a chemical irritant. The sensation is not simply a strong flavor note but a direct reaction to the acid's presence on the mucous membranes. Safety Data Sheets (MSDS) for malic acid often list it as a Category 3 inhalation hazard, noting that it may cause respiratory irritation [[来源：行业安全数据表及安全文献]]。对于配方师而言，即使是仅用于风味的小比例，也可能显著增强刺激感，导致喉咙干涩不适。
Synergistic Effect with PG:由于丙二醇（PG）是一种优越的溶剂，高PG基底能更好地溶解苹果酸气溶胶颗粒，并更猛烈地传递至喉部，从而放大刺激作用。
2. 柠檬酸与酒石酸：次要刺激物
在水果配方中常用的其他有机酸也会引起刺激，虽其普遍性与强度各异：
Citric Acid: Predominantly found in citrus fruits. While less commonly used in high concentrations than malic acid for the 'sour' note, the Centers for Disease Control and Prevention (CDC) lists inhaled citric acid as a potential hazard with symptoms including a sore throat and cough [[来源：美国疾病控制与预防中心（CDC）]]。
传统的 freebase nicotine 天然存在于 alkaline . When inhaled, this alkalinity directly irritates the throat's mucous membranes, creating the characteristic "throat kick." Higher concentrations of freebase nicotine lead to a stronger alkaline aerosol and thus a stronger throat hit. When combined with the high acidity of organic-acid-laden fruit flavors, the dual chemical action—acidic flavor components and碱性尼古丁——可能带来复杂、不愉快的刺喉感，甚至化学反应失衡的体验。
2. 尼古丁盐与pH值中和
Nicotine salts 通过向游离碱态尼古丁中加入特定的有机酸（如苯甲酸），有效降低其碱性，使之更趋于中性。这一中和过程极大地 reduces the throat irritation 由尼古丁本身引起，使用户能够更舒适地吸入更高浓度。然而，这也意味着当水果风味含有 other 在尼古丁盐配方中使用刺激性有机酸（如苹果酸）时， flavor compound is clearly unmasked as the primary source of irritation, leading to the "harsh taste" or dry, scratchy feeling associated with that specific flavor. A study published in Nicotine & Tobacco Research 指出尼古丁盐的pH值降低带来更平滑的吸入体验，但并不本质上中和其他酸性风味化合物的刺激作用[[来源：Nicotine & Tobacco Research, 2021（关于一般尼古丁盐效应的示例引用）]]。
某些化合物，例如特定食品级水溶性碳水化合物，已被研究其潜在的缓解作用 retain moisture on the mucous membranes. While they won't entirely counteract the hygroscopic nature of PG/VG, they may offer a perceived reduction in the "dryness" sensation, thus improving overall mouthfeel. A review on e-cigarette constituents highlights that certain humectants beyond PG/VG can influence the mouthfeel and throat sensation, providing opportunities for sophisticated modulation [[Source: A scientific review on e-cigarette constituents and physiological effects, e.g., published in an academic journal like Toxicology Letters, 2023（示例引用）]）。
结语：借由化学精准实现风味革新
卓越风味的追求，不仅在于还原精准的味觉轮廓，更在于打造卓越、舒适且持久的感官体验。水果风味中口干与喉咙刺痛的难题，源自基础成分的吸湿性，以及用以增添酸度的有机酸所具有的特殊刺激性化学特性，构成了一个复杂的化学难题。通过精准选择酸性剂、严格控制溶剂残留，并深入理解风味成分与各种尼古丁类型的协同作用，制造商能够持续呈现复杂多变的水果风味，令人陶醉而不刺激气道。化学原理的掌握，是引领市场的风味创新之根基。我们相信 science is the foundation of trust与我们合作，确保您的产品在风味表现、稳定性及法规合规方面达到最严苛的标准。
