Using an anti-yellowing shampoo all the time is not generally recommended. These shampoos are specifically designed to neutralize yellow or brassy tones in blonde or lightened hair, and they contain pigments that deposit on the hair to combat these unwanted hues. While they can be effective in maintaining a cool or ashy tone, frequent use may lead to the following issues:

1. Dryness: Anti-yellowing shampoos often contain pigments that can be drying to the hair, especially when used consistently. Overuse can strip the hair of its natural oils and cause dryness, brittleness, and breakage.
2. Over-Toning: Continuously using an anti-yellowing shampoo can deposit too much purple or blue pigment, potentially giving your hair a lavender or greyish tinge, especially if your hair is already light enough.
3. Buildup: With repeated use, the deposited pigments may accumulate on the hair, creating buildup that can dull the shine and affect the overall appearance of your hair.
4. Color Fade: Frequent use of any shampoo, including anti-yellowing ones, can hasten the fading of hair color, especially if it's artificial.

The best practice is to alternate between an anti-yellowing shampoo and a regular, moisturizing shampoo. Use the anti-yellowing shampoo once or twice a week, depending on how quickly the yellow tones return and the condition of your hair. Pay attention to the needs of your hair— if it starts to feel dry or looks over-toned, reduce the frequency of use.

It's also essential to use a deep conditioner or hair mask regularly to replenish moisture and maintain the health of your hair, especially if it has been chemically treated. Always follow the instructions provided with the specific anti-yellowing shampoo you're using and consult a professional stylist for personalized advice based on your hair's unique characteristics.