Short answer: scientific consensus statements are formed when experts review a body of evidence, assess the strength and limits of that evidence, and agree on what can responsibly be said at that time.
A consensus statement is not a vote on reality. It is a formal attempt to summarise the current state of knowledge. It may come from a scientific society, national academy, public health body, standards organisation, or expert panel. The strongest statements explain not only what is known, but also what remains uncertain.
What the process usually involves
Experts define the question, review relevant studies, assess quality, discuss disagreements, and draft conclusions. Some processes use systematic reviews. Others use structured expert panels. Good consensus work should manage conflicts of interest, include relevant expertise, and make the reasoning visible.
Consensus does not require every scientist to agree. It means that, among qualified experts considering the evidence, there is a broad and defensible position. Minority views may still exist, but they need evidence strong enough to challenge the wider conclusion.
How readers should use consensus
Consensus is most useful when a topic is complex and the public cannot realistically inspect every study. It is not infallible. Scientific consensus can change when evidence changes. But dismissing consensus simply because it is consensus misunderstands how expertise works.
A good reader asks: Who wrote the statement? What evidence did they review? Did they explain uncertainty? Were conflicts disclosed? Has the statement been updated? Consensus is not a substitute for evidence. It is a disciplined summary of evidence.