Background:
Worldwide, 5000 billion cigarette butts, containing more than 4000 toxic chemicals, are estimated to be each year littered. If the deleterious health impacts of smoking are well known, the roles of cigarette butts require clarification. Indeed, this pollution could have repercussions on health and the environment.

Objectives:
We aimed to review all main impacts of cigarette-butt pollution on human, animal, vegetal and environmental health.

Methods:
All electronic databases (from 1948 to March 2020) were searched with a combination of keywords related to cigarette butts and to human, animal, vegetal or environmental health.
Two independent reviewers selected studies of any design and in any language, using original data and investigating the associations between cigarette butts and human, animal, vegetal or environmental health. The selection was performed from abstracts and titles and pursued by reviewing and extracting data from the full text of potentially eligible studies.

Results:
After a detailed screening of 98 entire studies, 63 studies were identified. In some studies, nicotine poisoning or occlusive syndrome were described in young children and domestic animals. Other studies showed also river, ocean or coastal pollution by metals, polycyclic aromatic hydrocarbons or nanoparticles with toxicities on animals and plants, impacting the entire food chain down to humans. A few studies highlighted toxicity on species resistant to traditional insecticides (malaria vectors) and indicated that even rats were avoiding areas polluted by cigarette butts. Finally, the majority of studies reported pollution on all continents, either in urban or coastal regions, while cigarettes butts are not quickly biodegradable.

Conclusion:
Deleterious impacts of cigarette butts on human, animal, vegetal and environmental health are beginning to be described in the literature. The ubiquitous and growing nature of this pollution must raise concern among the civil societies and government in order to intensify the fight against smoking.