Yes, in the lab. The vapour from a nicotine-free vape is still propylene glycol and vegetable glycerine, and those two alone, with no nicotine and no flavour, thickened airway mucus and slowed the cilia in human airway cells and in sheep [3][4][5]. Nicotine adds a second hit of its own [6], so going to 0 mg removes one cause, not the carrier.
For the full mechanism, start with why mucus sits in your throat from vaping; if the mucus is new since you cut down, read what happens to the mucus after you cut down. This post is general information, not medical advice.
Does zero-nicotine vaping cause mucus?
Two studies asked exactly this. In the first, human small-airway cells in a dish got 15 puffs of nicotine-free vapour. Twenty-four hours later they had made more IL-6, an inflammatory signal, and held more MUC5AC, the main gel-forming protein in mucus, inside the cells [1]. In the second, a 50/50 PG/VG liquid at 0 or 24 mg/ml nicotine was vaped onto an airway cell line, primary human nasal cells and nasal tissue. With or without nicotine, MUC5AC went up, and adding nicotine did not raise it further [2].
Plain words: with no nicotine in the vapour, cells in a dish still made more of the protein that mucus is made of.
Why does my vape give me mucus if there is no nicotine? PG, VG and flavourings
Propylene glycol
PG is a humectant: it attracts and holds water, which is why it dries the mouth (see the dry-mouth post). Deeper down, pure PG aerosol with no nicotine raised mucus concentration, reduced ciliary beating and inhibited the BK channel, one of the channels that keeps the airway surface wet, in human bronchial cells and in sheep [5].
Vegetable glycerine
The only human data is small. Sixteen never-smokers vaped nicotine-free, flavour-free PG, VG or PG/VG for seven days. Every volunteer in the VG group had higher IL-6, IL-8 and MMP-9 in nasal cells and more MUC5AC in nasal fluid after the week, but the VG group was six people, with three or four in each measurement, and the authors say the sample was too small to test statistically. Call it preliminary. In sheep, five days of VG aerosol raised the solids in tracheal mucus, which is mucus getting thicker [3].
PG and VG together
The 50/50 mix was the worst case. One hundred puffs a day for seven days, no nicotine, no flavour, lowered CFTR, ENaC and BK channel activity and ciliary beat frequency in human bronchial cells, raised MUC5AC, lowered MUC5B and increased mucus solids in sheep [4].
Flavourings
Diacetyl and 2,3-pentanedione, two common flavouring chemicals, turned down cilia-building genes and reduced the number of ciliated cells in human bronchial cells within 24 hours, at levels the Harvard team calls low [8][9]. Fewer cilia, the same mucus to move.
High VG and phlegm production: PG or VG?
Vaping forums split on this. Some blame high-VG liquids and the denser vapour; others get a dry throat from PG and swear by VG. The studies say both do it: PG concentrated the mucus and slowed the cilia [5], VG concentrated it too [3], and the mixture did worst in the 2024 study [4]. No ratio is the mucus-free one; the sticky mucus post explains why concentrated mucus feels stuck. We do not give tips for vaping better; the lever is exposure.
So does switching to 0 mg stop the mucus?
It removes the nicotine effect. In the 2019 sheep and cell study, vapour with nicotine shrank the liquid layer the cilia beat in and thickened the mucus in human airway cells, and slowed mucus transport in sheep, more so at higher nicotine doses, through TRPA1, an irritant sensor in the airway lining [6]; the American Lung Association summarised it as nicotine vapour creating "more viscous phlegm" [10]. Take the nicotine out and that part goes.
Less is not none. The PG and VG studies above were all run without nicotine, and a 2025 study found that an unflavoured 30:70 PG:VG liquid with nicotine slowed the cilia and left visible defects in their structure under the electron microscope [7]. Only no vapour is none, and then the cilia recover over the following weeks; the science page has the recovery studies.
When to see a doctor
See a doctor for blood in what you cough up, fever, chest pain, wheeze or shortness of breath, a cough past three weeks, black mucus (no e-liquid should produce it), or asthma or COPD that feels worse. Anyone under 21 should not be vaping at all.
The vape reset
Clear is the morning step of the routine for the weeks after you cut down: mullein, menthol and peppermint drops. Supports respiratory comfort.* It is a dietary supplement, not a medicine, and it does nothing to mucus, a cough or the cilia; fewer puffs and time do.
Frequently asked questions
Do nicotine-free vapes still damage the lungs?
In the lab, nicotine-free vapour thickens mucus, slows cilia and switches on inflammatory signals in human airway cells and sheep [1][3][4][5]. Long-term human data on 0 mg liquids is thin: the volunteer study we could find had sixteen people and seven days [3].
Does vaping make you more phlegmy?
For about a quarter of people, yes. A 2023 meta-analysis found 24% of exclusive e-cigarette users reported phlegm, 21% cough and 37% dry mouth, with wide confidence intervals [11]. The surveys did not separate nicotine-free users.
Why does my vape give me mucus?
Three ingredients. PG concentrates the mucus and slows the cilia [5]. VG thickens the mucus [3]. Flavourings reduce the number of cilia [8]. Nicotine, if present, adds to all of it [6].
Why does vaping cause phlegm?
Phlegm is mucus that did not get swept away. Vapour makes the cells produce more of it [1][2] and the cilia move it more slowly [4][6], so it pools in the throat by morning.
Does VG cause bronchitis-like symptoms and phlegm?
A recurring vaping-forum question, and the lab partly backs it: VG aerosol raised inflammatory markers and mucus solids in sheep and, preliminarily, in a handful of volunteers [3]. "Bronchitis-like" is a doctor's call; a cough with phlegm past three weeks gets checked.
Can quitting vaping cause mucus?
Yes, for the opposite reason. Once the vapour stops, the cilia speed back up and bring up what sat there, so there is often more mucus for a few weeks before less; the cough guide covers how long and the colours. Free help with quitting is at Smokefree.gov and 1-800-QUIT-NOW [12].
Does Clear or any Cilia Labs product do anything to mucus?
No. Clear supports respiratory comfort.* It has no effect on mucus, cough or the cilia. What changes the mucus is fewer puffs and time.
Sources
- Gellatly S, Pavelka N, Crue T, et al. Nicotine-Free e-Cigarette Vapor Exposure Stimulates IL6 and Mucin Production in Human Primary Small Airway Epithelial Cells. Journal of Inflammation Research. 2020;13:175–185. https://doi.org/10.2147/JIR.S244434 (PMC7170627)
- Song SY, Na HG, Kwak SY, Choi YS, Bae CH, Kim YD. Changes in Mucin Production in Human Airway Epithelial Cells After Exposure to Electronic Cigarette Vapor With or Without Nicotine. Clinical and Experimental Otorhinolaryngology. 2021;14(3):303–311. https://doi.org/10.21053/ceo.2020.01907
- Kim MD, Chung S, Dennis JS, et al. Vegetable glycerin e-cigarette aerosols cause airway inflammation and ion channel dysfunction. Frontiers in Pharmacology. 2022;13:1012723. https://pmc.ncbi.nlm.nih.gov/articles/PMC9549247/
- Kim MD, Chung S, Baumlin N, et al. The combination of propylene glycol and vegetable glycerin e-cigarette aerosols induces airway inflammation and mucus hyperconcentration. Scientific Reports. 2024;14:1942. https://doi.org/10.1038/s41598-024-52317-8
- Kim MD, Chung S, Baumlin N, et al. E-cigarette aerosols of propylene glycol impair BK channel activity and parameters of mucociliary function. American Journal of Physiology-Lung Cellular and Molecular Physiology. 2023;324(4):L468–L479. https://doi.org/10.1152/ajplung.00157.2022
- Chung S, Baumlin N, Dennis JS, et al. Electronic Cigarette Vapor with Nicotine Causes Airway Mucociliary Dysfunction Preferentially via TRPA1 Receptors. American Journal of Respiratory and Critical Care Medicine. 2019;200(9):1134–1145. https://pmc.ncbi.nlm.nih.gov/articles/PMC6888648/
- Durra A, Cherry C, Luo C, et al. Unflavored electronic cigarette exposure induces alterations in airway ciliary structure and function. Respiratory Research. 2025;26:223. https://doi.org/10.1186/s12931-025-03302-w
- Park HR, O'Sullivan M, Vallarino J, et al. Transcriptomic response of primary human airway epithelial cells to flavoring chemicals in electronic cigarettes. Scientific Reports. 2019;9:1400. https://pmc.ncbi.nlm.nih.gov/articles/PMC6358614/
- Harvard T.H. Chan School of Public Health. Common e-cigarette chemical flavorings may impair lung function. 1 February 2019. https://hsph.harvard.edu/news/common-e-cigarette-chemical-flavorings-may-impair-lung-function
- American Lung Association. Another Gross Reason to Put Down the E-Cigarettes. https://www.lung.org/blog/another-gross-reason
- Alqahtani MM, Alenezi FK, Almeshari MA, et al. E-cigarette use and respiratory symptoms in adults: A systematic review and meta-analysis. Tobacco Induced Diseases. 2023;21:168. https://doi.org/10.18332/tid/174660
- Smokefree.gov. Speak to an Expert (1-800-QUIT-NOW). National Cancer Institute. https://smokefree.gov/tools-tips/speak-expert
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. Cilia Labs products are for adults 21+.