When you build a web application in PHP, one of the first things you’ll deal with is how to store data across multiple pages. This is where sessions and cookies come into play.

At first glance, they might seem similar — both help you keep track of a user. But under the hood, they work very differently.

In this blog, we’ll break it all down in simple terms — what they are, how they differ, and when you should use one over the other.

What Are Cookies?

Cookies are small pieces of data stored on the user’s browser. When someone visits your website, you can place a cookie in their browser, which gets sent back to the server with every request.

In the example above, we’re storing the name “JohnDoe” in the user’s browser for 7 days. 

Key Points:

• Stored on the client (browser)

• Can store up to 4KB of data

• Can have a custom expiration time

• Visible and editable by the user (less secure)

What Are Sessions?

Sessions, on the other hand, store user data on the server. Each visitor gets a unique session ID, which is usually saved in a cookie on their browser. This session ID is then used to fetch the correct data from the server.

Here, we’re starting a session and storing a value on the server. No sensitive data is sent to the browser.

Key Points:

• Stored on the server

• Can store larger and secure data

• Automatically expires when the browser is closed (unless customized)

• Not visible to the user (more secure)

Main Differences: Sessions vs Cookies

When to Use What?

Use Cookies When:

• You need to remember non-sensitive data (e.g., theme preference, language setting)

• You want data to persist even after the browser is closed

• You don’t want to depend on server storage

•  

Use Sessions When:

• You’re dealing with user authentication/login

• You want to store sensitive or dynamic data

• You need the data only during a visit (e.g., shopping cart)

A Real Life Example:

Let’s say you're building an eCommerce site:

• Use a session to store the shopping cart details, because you don’t want people to edit the cart data from their browser.

• Use a cookie to remember their preferred currency or language, so next time they visit, the site loads their preferences instantly.

Cookies and sessions are both essential tools in PHP for managing user data. Knowing when and how to use them makes your application more secure, faster, and user-friendly.

Think of cookies as notes left in the user's browser, and sessions as records stored in your system. Use each wisely depending on what kind of data you're handling.