What is a hashtag?

A hashtag groups content by topic. If you write #sourdough in a caption, the post can be found alongside others that carry the same tag. The tag is just text: nobody owns it, and anyone can start one. A hashtag can be a topic (#houseplants), a place (#lisbon), an event or a community.

• Write it without spaces. Capitalising each word, as in #HomeBakers, is easier to read and is commonly recommended for screen readers.
• Letters and numbers are fine. Instagram’s Help Center says numbers are allowed, but spaces and special characters, like $ or %, won’t work.
• A hashtag can be popular and still useless to you if the people using it are not your audience.
• Instagram’s Help Center says you can use up to 5 tags on a post, and that if you include more than 5 on a single photo or video, your comment won’t post. It doesn’t say what Instagram rewards, so judge that from your own insights.
• Posts from public accounts appear on the hashtag page, and the Help Center says posts tagged by people with private profiles won’t appear publicly there. You can only tag your own posts.

Meta’s Instagram Platform documentation for hashtag search describes a way for an app, working for a Business or Creator account, to find public media that carries a given hashtag. The documentation lists these limits.

The documentation also says it can return the most recent and the top media for a hashtag. In plain terms: an approved tool can research what is being posted under a tag, but it cannot reply to those posts for you.

• Mixing a disclosure into a pile of tags. The FTC’s influencer guide says not to bury a disclosure in a group of hashtags or links.
• Using a tag you never checked. Search it first to see what else sits under it.
• Treating a comment keyword as a hashtag. A word like GUIDE that triggers an automatic reply is plain text with no # needed.