Deep Conditioning
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A: Deep conditioning really only means that you are giving the hair a chance to absorb as much moisture and protein as possible.
But you can give your hair a deep conditioning at home with things you probably already have available. For instance, mayonnaise is a great deep conditioner as it has egg protein and oil for moisture.
Simply apply the mayo to the hair, wrap with plastic or use a cap and allow it to sit for 15 to 20 minutes. Rinse the hair with warm water and use a gentle shampoo afterward (otherwise, your hair will start to smell like spoiled mayo after a bit). The result will be soft and shiny hair.
You can also use things like olive oil, bananas (mashed to a pulp), avocadoes (mashed), or even your everyday hair conditioner. With the other foodstuffs, you do want to shampoo after rinsing, but you could use the after-shampoo conditioner and simply rinse it out with warm water.
Deep conditioning is best done once a week (or every 5-7 shampoos).
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See also:
Hair conditioners and conditioning treatments
Can you use a hair conditioner as a gel after drying?
Is it possible to wash hair with conditioner only?
Basic hair care