Polylactic Acid (PLA) is a widely used thermoplastic and the preferred material for many desktop 3D printing applications. This polymer is a bioplastic, derived from renewable sources, most commonly fermented plant starch from crops like corn or sugarcane. PLA’s appeal stems from its ease of use, low odor during processing, and perception as an environmentally conscious choice. However, determining if PLA is truly non-toxic is complex and depends heavily on its purity, how it is processed, and the final application of the printed object. A complete safety evaluation must consider the material’s inherent composition, risks introduced during manufacturing, and potential hazards associated with its end use.
Understanding PLA’s Inherently Low Toxicity
The fundamental safety of Polylactic Acid originates from its chemical structure as a polymer of lactic acid. Lactic acid is a substance naturally produced and metabolized by the human body. This inherent biocompatibility is the primary reason pure PLA is generally regarded as a low-toxicity material.
The material’s safety profile is supported by its long history of use in the medical field. PLA and its copolymers have been utilized for decades in bioabsorbable medical devices, including dissolvable sutures, screws, and drug delivery systems. Pure PLA has also received “Generally Recognized As Safe” (GRAS) status from the U.S. Food and Drug Administration (FDA) for certain food-contact applications. Migration studies show that any compounds released are primarily lactic acid and lactide, which are not considered a significant risk to health.
Potential Airborne Risks During 3D Printing
While pure PLA is inherently safe, heating the filament during 3D printing introduces potential airborne risks. Fused Filament Fabrication (FFF) printers melt the plastic at high temperatures, causing the release of airborne contaminants. These contaminants fall into two main categories: Volatile Organic Compounds (VOCs) and Ultrafine Particles (UFPs).
UFPs are microscopic solid particles, typically less than 100 nanometers in diameter, which are small enough to be inhaled deeply into the lungs. Studies show that while PLA releases fewer UFPs than other common filaments like ABS, the emission rate is still significant and comparable to other indoor activities like cooking. The primary VOC released from PLA is lactide, the monomer of lactic acid.
Exposure to these emissions is a concern, especially when printing in unventilated or small spaces. The most effective mitigation strategy is proper ventilation, such as operating the printer under a dedicated exhaust hood or in a well-ventilated room that directs air outdoors. Caution is advised when operating desktop 3D printers without combined gas and particle filtration systems, particularly for users with respiratory sensitivities.
Evaluating Safety in Finished PLA Objects
The safety of a finished PLA object shifts the focus from airborne risks to the potential for chemical leaching and microbial contamination during use. The non-toxic status of the raw polymer can be compromised by additives used in the filament manufacturing process. Many colored PLA filaments contain pigments, dyes, or processing aids that may not be food-safe or approved for human contact. Users should prioritize natural or undyed filaments for any sensitive application and consult the Material Safety Data Sheet (MSDS) provided by the manufacturer to verify the safety of all incorporated components.
The printing hardware itself can introduce contaminants. For example, brass nozzles commonly used in 3D printers may contain trace amounts of lead, which can contaminate the molten plastic as it is extruded. Using a stainless steel nozzle can eliminate this specific risk of heavy metal contamination.
The porous nature of FFF 3D-printed parts presents another significant safety challenge, particularly for items intended for food contact. The layer lines inherent to the printing process create microscopic crevices where moisture and food particles can become trapped. These micro-cracks are difficult or impossible to clean effectively, providing an ideal breeding ground for bacteria and other pathogens.
For this reason, PLA objects are generally not recommended for long-term food storage, repeated use with food, or items that require sanitization in a dishwasher. PLA’s low heat deflection temperature means it will easily deform in a dishwasher or when exposed to hot liquids. To safely use a PLA print with food, it is often necessary to apply a food-safe epoxy or sealant to create a smooth, non-porous barrier over the entire surface.