Secondhand smoke (SHS) from cannabis is the smoke exhaled by a user and the smoke released from the burning end of the product. This exposure introduces the pregnant individual and the developing fetus to a complex mixture of potentially harmful chemicals. The developing baby is highly sensitive to external environmental factors during pregnancy. Minimizing all non-essential chemical exposures is a fundamental public health recommendation for a healthy pregnancy outcome. This article examines the known risks associated with inhaling secondhand cannabis smoke and outlines practical steps for avoidance.
What Secondhand Cannabis Smoke Contains
Secondhand cannabis smoke is a complex aerosol containing numerous compounds resulting from the combustion of plant material. A primary concern is Tetrahydrocannabinol (THC), the psychoactive component, which becomes airborne and can be inhaled by others nearby. Studies show that non-smokers exposed to dense, unventilated smoke can absorb enough THC for it to be detectable in their blood and urine.
The smoke also contains many toxic chemicals found in secondhand tobacco smoke, including fine particulate matter, carbon monoxide, and polycyclic aromatic hydrocarbons (PAHs). Fine particulate matter is concerning because it travels deep into the lungs, entering the mother’s bloodstream. Some toxins, such as ammonia and hydrogen cyanide, have been found in higher concentrations in cannabis smoke than in tobacco smoke.
Impact on Fetal Development
The chemicals absorbed by the mother can cross the placental barrier, the organ responsible for nutrient and waste exchange between mother and fetus. The fat-soluble nature of THC allows it to readily pass through the placenta and enter the fetal bloodstream. This transfer means the developing baby is directly exposed to both psychoactive components and combustion toxins.
Exposure to these substances is associated with several adverse outcomes related to physical and neurodevelopmental health. Research suggests an increased risk of low birth weight and premature birth. Low birth weight can complicate the newborn period and potentially require extended hospital care.
The developing brain is especially vulnerable to chemical exposure during gestation. Studies have linked prenatal cannabis exposure, including secondhand smoke, to long-term neurodevelopmental effects. These findings include potential issues with attention, memory, executive function, and lower scores on tests of visual problem-solving and visual-motor coordination in children later in life.
The Risk of Thirdhand Exposure
Thirdhand smoke (THS) represents the chemical residue left behind on surfaces after cannabis smoke has cleared. This residue is a combination of fine particles and gases that settle on clothing, furniture, carpets, and walls. THC adheres strongly to these indoor surfaces, resulting in prolonged environmental contamination. Exposure occurs through skin contact, ingestion, and the inhalation of chemicals that off-gas back into the air over time. The residue contains toxic compounds, including some that are known to be cancer-causing, similar to those found in tobacco THS.
Strategies for Avoiding Exposure
The most effective strategy for complete avoidance is establishing a strict, 100% smoke-free environment. No smoking of any substance should occur inside the home, car, or any enclosed space shared by the pregnant individual. Partners and household members who use cannabis should smoke exclusively outside.
Smoking near an open window or in a separate room does not prevent exposure, as air currents carry particulates and gases throughout a shared space. After smoking outside, individuals should change their outer clothing and wash their hands and face before returning inside to minimize transferring thirdhand residue. For existing thirdhand smoke contamination, regularly washing all fabric items and thoroughly cleaning surfaces and floors can help reduce the residual chemical load.