Why Does the Smoke from Weed Look Blue?

Posted on October 7, 2022 by Munchies

Blue smoke rising from a joint may initially appear enigmatic or concerning, causing one to question whether something unexpected is occurring. However, this phenomenon is not as mysterious as it seems and does not indicate the presence of harmful or foreign substances in the cannabis. Instead, it is a natural occurrence explained by science. And today, we’ll demystify all the haze behind the blue smoke.

Key Takeaways 

• Blue smoke should not be used to judge the quality of cannabis; factors like combustion temperature and chemical composition affect its appearance.
• The blue color of cannabis smoke is due to Rayleigh scattering, where shorter wavelengths like blue light are scattered more by small particles.
• The blue tint of smoke is purely visual and does not indicate the higher quality or Delta 9 THC content in cannabis.
• Inhaled smoke turns from blue to white when exhaled due to increased particle size and moisture, explained by Mie scattering.
• Cannabis smoke shares chemical similarities with tobacco smoke, containing potentially harmful compounds and carcinogens that can pose health risks.

Understanding Blue Smoke From Weed

​The blue smoke from cannabis is primarily a visual phenomenon explained by Rayleigh scattering, and it does not necessarily indicate any specific quality or characteristic of the cannabis itself.​ 

The Law of Rayleigh Scattering is pivotal in explaining why smoke appears blue. In essence, this law deals with the scattering of light by small particles compared to the wavelength of light. The short wavelengths, which constitute blue light, are scattered more than the longer red wavelengths. 

Consequently, when sunlight interacts with smoke particles, the smoke appears bluish. This scattering effect is predominant in the sidestream smoke of a joint — the smoke that emanates from the lit end rather than that exhaled — because it involves smaller particulates that scatter light to give a blue tint.

When it comes to joints, blunts, pipes, or whatever else you’re smoking, the same principle applies. A short wavelength is caused when the sun and the smoke particles collide, giving it a blue tone that might make you wonder what in tarnation is happening. It’s a fluke of physics that leads to a cool visual experience, especially if you’re tripping.

The Law of Rayleigh Scattering Explained 

Basic Principles

Rayleigh scattering occurs when light interacts with small particles, typically particles that are less than about 1/10th the wavelength of the light. In this scenario, the scattering of light is inversely proportional to the fourth power of the wavelength. This means shorter wavelengths (such as blue and violet) are scattered much more than longer wavelengths (such as red).

During Rayleigh scattering, the oscillating electric field of a light wave induces movement in the charged particles (such as electrons) within a scattering particle. This movement creates a small radiating dipole that emits scattered light. The scattered light is predominantly elastic, retaining its original frequency and energy.

Effects and Implications

• Color of the Sky—The sky’s blue color results from the scattering of sunlight by molecules in the Earth’s atmosphere. Due to its shorter wavelength, blue light is scattered more than other colors, so it appears blue from the ground.
• Wavelength and Polarization – The Rayleigh scattering law also predicts the polarization of scattered light and the pattern of scattering intensity based on direction. It shows symmetric patterns for forward and backward scattering from single particles, accounting for the observed polarization in the scattered light.

The Transition from Blue to White Smoke

While the smoke observed as blue during combustion is fascinating, the color transition upon exhalation prompts further investigation. Once inhaled, the smoke interacts with the lungs, which become coated with moisture and other substances, causing the particles to increase. 

As a result, the exhaled smoke loses its blue tint and appears white, similar to clouds, which are white because larger droplets scatter light equally across all wavelengths. This transformation aligns with the Mie scattering phenomenon, resulting in a whitish smoke that lacks the previous blue tint. 

Considerations and Myths

There are several myths and misunderstandings regarding blue smoke and cannabis. Some believe that the presence of blue smoke can indicate higher quality cannabis or a higher Delta 9 THC content, but these beliefs are not scientifically substantiated. 

Multiple factors, including the chemical composition of the smoke, combustion temperature, and the presence of certain terpenes, can influence the appearance of blue smoke. Additionally, the color of smoke should not be the sole indicator of cannabis quality. Ensuring cannabis is sourced from a reputable supplier is crucial to avoid possible contaminants that might affect both the color of the smoke and its safety.

Final Thoughts 

​The Law of Rayleigh Scattering explains the blue appearance of smoke from burning weed, similar to why we perceive the sky as blue.​ While blue smoke from cannabis might appear visually distinct, it is a naturally occurring phenomenon rather than a sign of adulteration or danger.

However, it is essential to remain conscious of the potential health risks associated with the inhalation of cannabis smoke, which shares similarities with tobacco smoke in terms of chemical composition. Understanding both the science behind blue smoke and the implications of cannabis use is crucial for informed consumption.

(Disclaimer reminder: This article is not medical advice. It is based on anecdotal user experience alone. If you are thinking about incorporating cannabis (delta-8 THC, delta-9 THC, CBD, etc) into your medicinal routine, please consult a healthcare professional. Do not stop taking any prescribed medications without first consulting your doctor.)

Disclaimer: This article reflects the laws of the United States at the time it was written. Because cannabis laws in the United States laws are subject to change at any time, please make sure that you are always staying up to date on your federal, state, and local county’s cannabis laws. Additionally, we are NOT encouraging anyone to break the law––we are simply showing people ways to legally and discreetly bring their cannabis products along with them on their travels so that they may have access to those products when they reach their intended destination.