Unlike some online advertising platforms, Facebook audiences do not change very quickly.
Most of the people that are included in a particular targeting option will still be there in 6 or 12 months’ time.
Because of this, if you promote the same ad to the same group of people for an extended period of time, ad fatigue will almost certainly become an issue - and when it does, the effectiveness of your Facebook ad campaign, and how much it costs to reach people, is going to be significantly impacted.
Fortunately, there are measures you can take to help overcome Facebook ad fatigue, and ensure your results don’t suddenly drop off a cliff.
Here are nine ways to improve your approach.
1. Use the Reach Objective
When you create a Facebook ad campaign there are a number of campaign objectives to choose from.
One of them is the Reach objective:

The Reach objective is designed to get your ad in front of as many people as possible, which is unlike other campaign objectives such as 'Conversions' (which serves your ad to people that are most likely to convert).
Using the Reach objective spreads your ad impressions over a larger number of people, which means it'll take longer for ad fatigue to set in.
2. Set A Frequency Cap
The Reach objective can be even more effective with a frequency cap.
Frequency caps limit how often people within your selected audience will see your ad.

Frequency caps are set at the Ad Set level in Optimization for Ad Delivery. The example above would limit the number of impressions to just one per week, per person.
This is a great way to prevent Facebook ad fatigue.
3. Advertise Content Alongside Other Offers
Advertising high-quality content is an effective way to warm up cold audiences - and it can also help combat ad fatigue.
Promoting a blog post or video alongside your main offer can deliver extra value to your target market, and buy you some more time.
This technique works best when the content is not promotional, or too closely related to the product or service being advertised.
4. Change Ad Creative
Facebook ad creative refers to the images, text and headlines that make up a Facebook ad. Changing these elements can give your campaign some extra life.
However, you need to make significant changes to your ad. It can’t look like a variation of the original, it needs to look like a brand new ad.
Changing the ad image and/or headline is the most effective way to do this. Here’s an example of two ads that look very different, but are promoting the same service:

And…

5. Change Ad Format
Sometimes changing your ad creative just isn’t enough. In which case, you can step it up a gear and change ad format.
I’m a massive fan of video ads on Facebook, and they are certainly underused.
A lot of advertisers could boost their results and overcome ad fatigue by creating video ad versions of winning image ads.
For example, this video ad is promoting my 5-Part Facebook Ad Template:

And even though they look very different, so is this image ad:

6. Regularly Change the Product or Service Being Offered
This one’s fairly obvious, but not a lot of Facebook advertisers do it. When a particular product or service is selling well, it can be really difficult to stop advertising it.
But regularly changing up your offer is one of the best ways to ensure that people don’t become bored with your ads.
This option isn’t available to every business. Some only offer one product or service and will have to use some of the other options listed in this article.
But if you offer a range of products or services, I would recommend that you regularly switch between them. And don’t wait until your results start to drop off before you do.
7. Use Holiday Themed Ads
Creating holiday-themed ads can make them more relevant and improve your results.
It also naturally keeps your advertising fresh - because there's only so long you can run a holiday promotion for.

Holiday-themed ads work incredibly well for certain businesses. People expect to take certain actions around holidays - they are prepared to buy presents at Christmas and chocolate at Easter. Tapping into this, where possible, can significantly improve your ROI.
8. Target a New (Lookalike) Audience
Just because a certain audience has become fatigued with your ads, that doesn’t mean that you have to abandon that campaign altogether.
There may well be other audiences that could also generate great results. One of the best ways to find these people is with a Lookalike Audience.
Lookalike Audiences consist of people that are very similar to another group of people - for example, you can create a lookalike audience that is based on your existing customers. The lookalike audience will then contain people that are very similar to those who have already purchased your products.
This is a fantastic targeting option, and often outperforms the original audience.
Below you can see the results from one of my campaigns.
Lookalike audience:

Original audience:

9. Keep Retargeting Budgets Small
Facebook ad fatigue can be a massive issue with retargeting campaigns.
Retargeting on Facebook is done by targeting custom audiences. Custom audiences can be created from a number of data elements, including customer lists, email lists and website visitors.
Custom audiences are nearly always significantly smaller than cold audiences, which means ad fatigue will set in a lot sooner. Keeping retargeting budgets small, prevents people within your custom audience being shown your ad too many times.
What counts as "small" for your retargeting campaigns will depend on your custom audience size. A great way to work out if your budget is too large, is to monitor your ad frequency:

If that Frequency number increases dramatically over a short period of time, your budget is too high.
Conclusion
Facebook ads can be a great way to raise awareness for your business and products, but ad fatigue is a real issue, and can end up working against you very quickly. Make sure you limit the potential impacts by following these tips.