What happens to your scalp when you wash your hair once a week mostly depends on your hair type and lifestyle. Washing your hair once a week can affect your scalp's oil production, skin barrier, and overall health—for better or worse.1

Benefits of Washing Your Hair Once a Week

For many people, washing your hair once a week is convenient and helps improve scalp health.2 People with dry, curly, or thick hair types may only need to wash every one to two weeks.3 

Decreased Scalp Irritation and Dryness

Like your face, your scalp has oil glands that produce natural oils (known as sebum) to moisturize your scalp and hair. If your hair feels brittle and your scalp is dry and irritated, you're likely shampooing too often.1

Overwashing your hair strips away oil. Washing your hair once a week can help replenish natural hair oils that moisturize your hair and scalp, without causing excess greasiness. Proper scalp hydration is important to keep your scalp moisturized, nourished, and irritation-free.1

Less Greasiness

 If your scalp is dry but your hair is greasy, washing your hair only once a week may help regulate oil production.

It may seem counterintuitive, but if you have excessively greasy hair, you may be washing it too often. Overwashing strips away oils, and some reports suggest this may cause your oil glands to increase oil production to replenish lost moisture.1 This creates overly greasy hair while the scalp remains dry and irritated.4 

Healthier Scalp for Hair Growth

If you notice you're losing more strands of hair than usual, washing your hair less often may help. Extremely dry hair is more prone to breakage, and a dry scalp leaves you more susceptible to conditions and infections that prevent hair growth.1 

Washing your hair less can help the scalp retain oils that coat the hair shaft—resulting in stronger, shinier hair. These oils also create a protective barrier on your scalp to keep your skin healthy. Having a healthy scalp and hair follicles will help promote hair growth.56

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Negatives of Washing Your Hair Once a Week

Washing your hair only once a week isn't ideal if you have naturally oily skin, fine hair, use a lot of hair products, or are getting sweaty or dirty frequently.  

Potential for More Build-up and Irritation

Not washing your hair enough can cause excess oil and build-up—especially if you live an active lifestyle or have oily, fine hair. Washing your hair once a week can make your scalp more prone to a build-up of oil, bacteria, yeast, hair products, dead skin cells, and odor.1

This build-up can clog hair follicles and irritate your scalp. It can also lead to hair loss.7 You may also notice itchiness, flakiness, and hair that looks weighed down and greasy. To prevent buildup and oiliness, some people will need to wash their hair every one to two days.4

Increased Risk of Fungus and Skin Infections

An irritating build-up of sweat, oils, and dirt can also create the perfect environment for fungi and bacteria to grow on your scalp.8 Infrequent hair washing can give dandruff-causing Malassezia yeast more opportunity to overgrow and feed on oil. This overgrowth leads to an itchy scalp, odor, and flakes.1 

A scalp with excessive oil and yeast may also lead to a seborrheic dermatitis rash. This non-infectious skin condition can cause scaly, irritated patches on the scalp's oilier areas.9 Studies have found that more frequent washing is ideal for reducing flakes, yeast, and redness linked to seborrheic dermatitis.1 

How To Transition to Weekly Hair Washes

If you want to try washing your hair only once a week, be patient. It can take a few weeks for your scalp's oil production to regulate.

Some tips to transition to washing your hair once a week include:4

• Slowly decrease your hair-wash days: If you wash your hair daily or every other day, drop down to two to three days a week. Then, ease into one day a week. 
• Rinse between washes (as needed): If you're worried about odor and build-up, rinse your hair and scalp with water between washes, especially after workouts.10 
• Use dry shampoo sparingly: Choose a fragrance-free option made for your hair type and color. Only apply dry shampoo where you feel greasy and let it sit for a bit to absorb oil before brushing it out.11
• Avoid homemade dry shampoos: Cornstarch, cocoa powder, and baking soda are more likely to clog pores and irritate your scalp. Bacteria also love to feed on cornstarch, which can cause odor.11
• Focus on cleansing your scalp: Gently massage shampoo directly onto your scalp with your fingertips, then let it run down your hair when you rinse. Only use conditioner on the ends of your hair.
• Rinse and repeat: On hairwash days, try a clarifying shampoo to remove build-up. After, wash again with a more moisturizing shampoo suited to your hair type.12