It really depends what type of extensions you have.
Full head weave: Your hair should have been washed, conditioned and neatly corn rowed with synthetic hair. Some people use wool to stitch the weave on, this is not good because wool traps and attracts oils and moisture and will eventually starts to smell. Your hair should remain tidy underneath your extensions. Try not to apply any grease based products to your own hair extensions (they won’t grow) or use any firm holding sprays, these contribute to your hair extensions becoming cloggy and heavy and eventually dirty. There is very little maintenance required for your hair underneath, because it is not being affected by any chemicals or continual grooming, so your hair is resting and growing. Try not to keep a weave-on in more than 8 weeks. I think it is a good idea to release your hair, have it washed and conditioned and then your weave reapplied. When your hair is in its natural state and resting, it will grow all by itself without any assistance. ...More >
Lace Wigs or Wigs: I do not advise using a wig cap for the same reason as using wool. I do not advise keeping your lace wig on continually for more than 2 weeks at a time if possible. You need to keep the area around your hairline clean and free from potential infection or skin discolouration or pigmentation problems. There is very little maintenance required for your hair underneath, because it is not being affected by any chemicals or continual grooming, so your hair is resting and growing. When your hair is in its natural state and resting, it will grow all by itself without any assistance.
Integrated Hair extension techniques such as strand by strand, integrated weave, hook and latch, micro ring track, clip-ins or weft bonded techniques. This means your hair is still exposed in between layers of hair extensions. It is best not to use any grease base products, but use a good quality leave in spray condition each morning and evening. Try to use a good quality brush that will groom from the root without pulling out your hair extensions, this will help to avoid matting. Wash your hair once or twice a week with a good quality shampoo for greasy hair. This shampoo type will moisture your hair without adding grease which might contribute to premature loosening of your extension. If you would like to know more about looking after your hair extensions