Difference Between Session and Cookies in PHP ?

Last Updated : 14 May, 2025

Both sessions and cookies are important for maintaining state and storing data in PHP. However, they differ significantly in terms of how and where they store data, their lifespan, security features, and use cases.

In this article, we will explore the key differences between sessions and cookies in PHP, focusing on their functionality, advantages, and limitations.

Difference Between Sessions and Cookies

Here is a detailed comparison between sessions and cookies in PHP based on various features:

Sessions	Cookies
Data is stored on the server.	Data is stored on the client’s browser.
Data is available as long as the session is active (until the browser is closed or the session expires).	Cookies can persist for a specified period, even after the browser is closed.
No significant size limit (limited by server resources).	Limited to approximately 4KB of data.
More secure because the data is stored on the server.	Less secure, as data is stored on the client’s machine.
The session lasts until the browser is closed or the session expires.	Cookies can have an expiry time set during creation.
Session data is only accessible on the server side.	Cookie data is accessible on both the client and server sides.
Can store sensitive information securely (e.g., user authentication).	It can be intercepted or manipulated if it is not encrypted.
Storing sensitive or temporary data (e.g., login credentials, shopping cart data).	Remembering user preferences, tracking users, or remembering non-sensitive information between sessions.
Supports transactions to ensure data integrity within the session.	No support for transactions, as cookies are stored on the client.
Maintains state over multiple pages by storing data in the session.	The stored data persists between sessions, allowing users to maintain their state across visits.

What Are Sessions in PHP?

A session in PHP is a way of storing information (in variables) to be used across multiple pages. Sessions are stored on the server and can hold large amounts of data. A session is identified by a unique session ID, which is typically stored as a cookie on the client’s browser. When the session is started using session_start(), PHP automatically associates the session ID with the corresponding session data on the server.

Features of Sessions:

Server-side storage: Sessions store data on the server, making them more secure.
No size limitations: Since the data is stored on the server, there are no size constraints like cookies.
Automatic data cleanup: PHP automatically removes session data when the session expires or the browser is closed.

What Are Cookies in PHP?

A php cookie is a small file stored on the client’s browser, containing data that can persist even after the user leaves the website or closes the browser. Cookies are created by the server using PHP's setcookie() function, and they are sent along with every HTTP request to the server.

Features of Cookies:

Client-side storage: Cookies store data on the client’s browser, which can be accessed by both the client and server.
Limited size: Cookies can only store up to 4KB of data.
Expiry control: You can set an expiration time for cookies, after which they are automatically deleted.

When to Use Cookies and When to Use Sessions

Use Cookies:

User Preferences: Store settings like language, theme, or display options.
Tracking User Activity: Track user behavior for analytics or personalization.
Non-Sensitive Login Info: Store "remember me" tokens for keeping users logged in.
Non-Sensitive Data: Store small, non-sensitive data that needs to persist across sessions.

Use Sessions:

Sensitive Information: Store sensitive data like passwords, authentication status, or payment details.
Temporary Data: Track data only for the current session, like shopping cart content.
User-Specific Data: Store personalized data that should be kept secure (e.g., user roles, preferences).
Access Control: Use sessions for verifying login status and ensuring secure access to pages.

Conclusion

In conclusion, both sessions and cookies serve important purposes in PHP, but they differ in terms of storage, security, and use cases. Sessions are more secure and suitable for storing sensitive user data, such as login information, and are ideal for managing user state across multiple pages. Cookies, on the other hand, are useful for storing non-sensitive data that needs to persist across sessions, such as user preferences or tracking information.

Difference between sessions and cookies in Express

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