As you download apps to your smartphone, you’re often met with requests from the app to access personal information, like your contacts, photos or current location. It also might ask to send you push notifications. Sometimes, especially if you have an Android phone, you must agree to them all just to use the app.

Some app permissions are common sense, such as allowing a camera app to use your phone’s camera. If you spend time on Facebook or Instagram, you probably upload snapshots of your friends and family. Naturally, the app for these services needs to be able to access your photos.

But other permissions are surprising. A highway traffic app might ask to view your contacts or have “full Internet access,” that is, the ability to upload and download data from your phone at any time, whether you are engaged with the app or not.

There might be a good reason an app needs to access your data round the clock — for example, a GPS app needs to read your location so a loved one can find you in case of an emergency. But a cute, time-wasting video game does not need to know your every step.

Some apps ask for the moon when it comes to permissions simply because they can. A few are more nefarious: They install hidden software known as “malware” that runs misleading advertising on the phone. 

These programs can attempt to access your cellular account and charge you monthly fees without your explicit knowledge. Smartphone marketplaces will ban an app once it gets enough complaints, but that can take time and often the damage is done. It really is a “user beware” world, as far as phone apps go.

If you are concerned about an app, delete it from your phone. If you find the app useful and want to review what information it gathers on you and your movements, here are the steps to take, depending on whether you have an Apple or Android phone.

Apple

Control privacy and tracking of your smartphone under Settings > Privacy. You can choose whether the app can use your contacts or access your photos, for instance. You can deny location data entirely by turning off GPS on your phone. To do that, go to Settings > Privacy > Location Services.

Turning off Location Services, however, can affect how certain apps work. Instead, reset all location and privacy settings at once by going to Settings > General > Reset and then tap “Reset Location & Privacy.” After that, if an app needs to use location services or wants personal data, it will ask you first before proceeding.

Android

Google’s Android operating system currently doesn’t allow users to choose which powers to give a single app (although it might in a future release). You either accept all permissions upon installing or you choose not to install the app at all. You can, however, review each app by going to Settings > Apps and then tapping each app. The permissions for each are at the bottom of the screen.

You also can reset all apps to their defaults at the Settings > Apps screen by tapping on the three vertical dots at the upper left of your phone’s screen. From there, choose “Reset app preferences” from the drop-down menu.

Greg writes about personal finance, business and technology. His work has appeared in Businessweek, Newsweek, Forbes, Bankrate and a variety of trade ​publications.