The rules surrounding when to use shampoos and conditioners are refreshingly straightforward: Always use shampoo, condition if your hair is dry, rarely use both. "Shampooing cleans by removing dirt and oil and is formulated to be gentler than regular soap," says Dr. Ryan Welters, Chief Medical Surgeon for the New England Center for Hair Restoration. "Conditioners leave behind a layer of lipids which protect hair from losing too much oil during the shampooing process." Still, different hair and scalp textures require different levels of shampooing and conditioning– and different products.

Short Hair
In general, short hair only requires a moisturizing shampoo, like Aveeno Pure Renewal ($7.49 for 10.5 fl oz). Conditioners weigh hair down and make the follicles all fall together, so if a short haircut is worn with a little volume and/or texture, you don't need it. The same goes for short hair that feels oily to the touch.

If your hair tends to feel dry – you know this if it is brittle and frizzy – or is styled neater and/or closer to the head, opt for the next level in strength – a 2-in-1 shampoo and conditioner like Mitch Double Hitter ($20 for 8.5 fl oz) to add a little more nourishing hydration.

Then there's short curly hair. "I always suggest using a moisturizing shampoo plus a conditioner for curly hair," says Kristan Serafino, celebrity stylist who works with Matthew McConaughey. Curls tend to be more brittle, dry, and frizzy than straight hair, a characteristic the moisture of a conditioner can help to keep under control.

Longer Hair
The longer the hair the more you'll tend to need a separate conditioner, says Serafino. Burt's Bees More Moisture Baoaban shampoo ($8 for 10 fl oz) and conditioner ($8 for 10 fl oz) are strong choices. Oils produced by the scalp that naturally descend along the follicles can't travel far enough to naturally hydrate ends. If you've got long and dry hair, condition your whole head everyday, but if you have long hair and a scalp that tends to produce a lot of oil, Dr. Welters advises, "you might find you need a conditioner every day, but only use it in the distal areas away from the scalp."

In all cases, it is important to chose a sulfate-free product. Sulfates make a product sudsy but also causes over drying which defeats the entire purpose of a conditioner. All products suggested here are free of sulfates.