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Should I Use Leave In Conditioner? A Cosmetic Chemist’s Insight

September 11, 2023


Verna Meachum

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With extensive experience in the beauty industry, I specialize in writing for curly hair care brands, websites, and magazines.

Not only do I have curly hair, but my children, friends, family members, and even friends who are professional curly hairstylists, each with their unique curly textures.

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I also partner with a friend who holds a Ph.D. in chemistry and works as an R&D Chemist, ensuring our content is scientifically accurate and help us navigate through the misinformation around curly hair care. 

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Last Updated on September 11, 2023 by Verna Meachum

“Should I Use Leave In Conditioner?” is a question many hair enthusiasts grapple with. In short, the answer is absolutely, especially if you’re seeking enhanced moisture, protection, and manageability for your hair.

Leave-in conditioners are formulated to provide prolonged hydration, detangle hair, reduce frizz, and offer protection against environmental stressors.

They’re particularly beneficial for those with curly, wavy, or dry hair types, as these tend to lose moisture more quickly. However, the key is to select a product tailored to your hair’s specific needs.

I consulted my friend who specializes in hair science and is a cosmetic formulator to understand the science behind leave-in conditioners. Together, we’ll explore their benefits and how they can elevate your hair care routine.

Understanding Leave-In Conditioners

Image of four leave in conditioners for curly hair for Should I Use Leave In Conditioner blog.

At its core, a leave-in conditioner is a hair care product designed to be applied after washing and left in the hair without rinsing. Unlike regular conditioners that you rinse out, leave-ins are formulated to stay in your hair, providing prolonged moisture and protection.

The Science Behind It

From a cosmetic chemistry perspective, leave-in conditioners are emulsions containing a blend of water, oils, and other beneficial ingredients. These components work synergistically to:

  1. Hydrate: They replenish the hair’s moisture content, which is essential for curly hair types that tend to be drier.
  2. Seal: Oils and silicones in the formula can help “seal” the hair cuticle, reducing frizz and adding shine.
  3. Protect: Many leave-ins offer protection against oxidation and environmental aggressors like UV rays and pollution.

Benefits for Curly Hair

Image of a magnified hair strand wrapped with substance for Should I Use Leave In Conditioner blog.

Curly hair, with its twists and turns, has a unique structure that makes it prone to dryness and breakage. Here’s why leave-in conditioners can be a game-changer:

  • Moisture Retention: Curly hair struggles to retain moisture. Leave-ins provide an added layer of hydration that lasts.
  • Detangling: The slip provided by these products can make detangling a breeze, reducing breakage.
  • Frizz Control: By “sealing” the hair cuticle, leave-ins can combat the dreaded frizz many curly-haired individuals face.
  • Styling Aid: Some leave-in conditioners can double as styling products, helping to define curls and reduce the need for multiple products.

Should You Use One?

If you have curly hair that’s prone to dryness, frizz, or breakage, a leave-in conditioner can be a valuable addition to your routine. However, it’s essential to choose a product suited to your hair type and needs. For instance:

  • Fine Hair: Opt for a lightweight, spray-on formula to avoid weighing the hair down.
  • Thick or Coarse Hair: A richer, cream-based leave-in can provide the necessary moisture and manageability.
  • Damaged or Color-Treated Hair: Look for leave-ins with proteins or reparative ingredients to strengthen and protect the hair.
  • Low Porosity Hair: Struggles to absorb products due to its tightly “closed” cuticles, leading to potential product build-up. Thus, it’s best to choose lightweight leave-in conditioners that hydrate and detangle without adding weight.

Incorporating a leave-in conditioner into your routine can lead to healthier, shinier, and more resilient hair. However, always be mindful of the quantity used to prevent product build-up.

Leave-In Conditioner vs. Traditional Conditioner vs. Deep Conditioner: What’s the Difference?

Navigating the world of hair care can sometimes feel like deciphering a complex puzzle, especially with the myriad of products available. Among them, conditioners of various types often raise questions:

What’s the difference between a leave-in conditioner, a traditional conditioner, and a deep conditioner? Let’s break it down from a cosmetic chemist’s perspective.

1. Traditional Conditioner (Rinse-Out Conditioner)

Image of the Shea moisture coconut and hibiscus conditioner for Should I Use Leave In Conditioner blog,

What is it?
A traditional conditioner, often referred to as a rinse-out conditioner, is applied to the hair after shampooing and is rinsed out after a few minutes.

Key Ingredients:

  • Cationic surfactants: These positively charged molecules bind to the negatively charged hair surface, smoothing out the hair cuticle.
  • Oils and silicones: Provide slip, shine, and some level of hydration by forming a protective barrier around the hair shaft. This barrier helps seal in moisture, preventing water loss from the hair’s internal structure. Additionally, they smooth out the hair cuticle, reducing frizz and enhancing light reflection, which contributes to the hair’s shine. On a molecular level, while some oils can penetrate the hair shaft to provide enhanced internal hydration, silicones mainly remain on the surface, offering external protection against environmental aggressors and mechanical damage.
  • Hydrating Ingredients, such as glycerin and propylene glycol.
  • Viscosity Boosting Agents, such as fatty alcohols.
  • Emollients, such as natural oils or butters, contain high molecular weight fatty molecules yet lack a greasy texture.
  • Proteins: Proteins and amino acids serve multiple roles: they boost the moisture levels in fibers, replenish lost proteins in hair, and enhance their attachment to surfaces.


  • Detangles hair, making it easier to comb or brush.
  • Smoothens the hair cuticle, reducing frizz.
  • Provides immediate softness and conditioning.

Used after every shampoo session, left on for 2-5 minutes, then rinsed out.

2. Deep Conditioner

Image of Mielle babssu and mint deep conditioner for Should I Use Leave In Conditioner blog.

What is it?
A deep conditioner is a more intensive treatment designed to penetrate deeper into the hair shaft, providing profound moisture and repair.

Key Ingredients:

  • Emollients, cationic conditioning actives, and cationic polymers.
  • Proteins: Help to strengthen and repair damaged hair.
  • Penetrative oils like coconut oil: These can enter the hair shaft, providing deep hydration.


  • Intensively moisturizes the hair.
  • Repairs damaged hair and strengthens weak strands.
  • Restores hair elasticity, reducing breakage.
  • Smoother hair surface.
  • Reduced frizz.
  • Shine.

Used once a week or bi-weekly, depending on hair needs. It’s left on the hair for an extended period (15-30 minutes, sometimes even longer under heat) and then rinsed out.

3. Leave-In Conditioner

Image of Briogeo farewell frizz leave in conditioner for Should I Use Leave In Conditioner blog.

What is it?
As discussed earlier, a leave-in conditioner is designed to be applied after washing and left in the hair without rinsing. They provide an extra boost of nourishment for your hair prior to styling.

Key Ingredients:

  • Lightweight oils and emollients: Provide hydration without weighing the hair down.
  • Humectants: Attract moisture from the environment to the hair.
  • Silicones (in some formulations): “Seal” in moisture and provide a protective barrier.
  • Conditioning Agents
  • Extracts


  • Prolonged moisture retention.
  • Protection against environmental aggressors.
  • Can act as a styling aid, especially for curly hair.

Applied to damp hair after washing and not rinsed out. It’s used as the final step in the washing routine or as a refresher between washes.

How to Properly Use a Leave-In Conditioner: A Step-by-Step Guide

Using a leave-in conditioner can be a game-changer for your hair, but it’s essential to apply it correctly to reap its full benefits. Here’s a step-by-step guide to ensure you’re getting the most out of your product:

1. Start with Clean Hair:
Before applying a leave-in conditioner, ensure your hair is clean. Wash your hair with a suitable shampoo and follow up with a rinse-out conditioner if needed.

2. Towel Dry Gently:
After rinsing out your shampoo (and traditional conditioner, if used), gently squeeze out excess water with your hands. Then, using a microfiber towel or a soft cotton t-shirt, blot your hair to remove more water. Avoid rubbing vigorously as this can cause frizz and breakage.

3. Section Your Hair:
Depending on the thickness and length of your hair, divide it into sections. This ensures even distribution of the product. For most people, 2-4 sections work well.

4. Apply the Leave-In Conditioner:

  • For Spray Formulas: Hold the bottle a few inches away from your hair and spray evenly onto each section. Ensure you cover the lengths and ends, which tend to be drier. This is one of my favorite leave in conditioning spray.
  • For Cream or Gel Formulas: Take a small amount of product in your palm, rub your hands together to warm and spread the product, and then apply it to each section. Start from the ends (which are the oldest and most fragile part of your hair) and work your way up, stopping a few inches from the roots unless your scalp is particularly dry.

5. Use the Right Amount:
Less is more when it comes to leave-in conditioners. Start with a small amount and add more if needed. Over-applying can weigh down your hair or make it look greasy.

6. Detangle:
Using a wide-tooth comb. detangling brush, or your fingers, gently detangle your hair, starting from the tips and working your way up to the roots. The slip from the leave-in conditioner should make this process easier and reduce breakage.

7. Style as Usual:
Once your hair is detangled and the product is evenly distributed, style your hair as you normally would. Whether you’re air-drying, diffusing, or using heat tools, the leave-in conditioner will act as a protective barrier.

8. Reapply as Needed:
Between washes, if you feel your hair needs a moisture boost or some frizz control, you can reapply a small amount of leave-in conditioner. Just remember to use it sparingly to avoid product build-up.

Pro Tip: If you have particularly fine hair or are worried about your hair looking weighed down, apply the leave-in conditioner before your rinse-out conditioner during your shower. This way, any excess product gets rinsed out, leaving just the right amount of moisture behind.

Remember, everyone’s hair is unique, so it might take a few tries to figure out the perfect amount and method for your hair type. With patience and practice, you’ll find the perfect balance that leaves your hair feeling soft, hydrated, and beautiful!

Precautions When Using Leave-In Conditioner

Image of the word "precaution" for Should I Use Leave In Conditioner blog.

While leave-in conditioners can be a boon for many hair types, especially those craving extra moisture and protection, it’s essential to use them wisely. Here are some precautions to keep in mind:

1. Avoid Overuse:
It’s easy to think that more product means more hydration, but overusing leave-in conditioner can lead to product build-up, making hair feel heavy, greasy, and limp. Always start with a small amount and add more if necessary.

2. Be Mindful of the Scalp:
Unless you have a very dry scalp, it’s best to avoid applying leave-in conditioner directly to the roots. This can lead to an oily scalp, reduced volume, and even potential build-up that can clog hair follicles.

3. Choose the Right Product for Your Hair Type:
Not all leave-in conditioners are created equal. Those with fine hair should opt for lightweight, spray-on formulas to avoid weighing the hair down. In contrast, those with thicker, coarser hair might benefit from creamier formulations.

4. Watch Out for Protein Overload:
Some leave-in conditioners contain proteins, which are great for strengthening hair. However, too much protein can make hair brittle and prone to breakage. If you’re using multiple products with protein (like shampoos, conditioners, and treatments), ensure you’re not overloading your hair.

5. Be Cautious with Silicones:
Many leave-in conditioners contain silicones, which can provide a smooth finish and protect the hair. However, some silicones are not water-soluble and can build up over time, requiring a clarifying shampoo to remove. If you’re following a silicone-free or sulfate-free regimen, read product labels carefully.

6. Conduct a Patch Test:
If you’re trying a new product or have sensitive skin, it’s always a good idea to conduct a patch test. Apply a small amount of the leave-in conditioner to the inside of your wrist or behind your ear and wait 24 hours. If there’s no reaction, it’s likely safe to use on your hair.

7. Store Properly:
Ensure you store your leave-in conditioner in a cool, dry place, away from direct sunlight. This helps maintain the product’s efficacy and prevents degradation of its ingredients.

8. Check Expiry Dates:
Like all cosmetic products, leave-in conditioners have a shelf life. Using an expired product can reduce its effectiveness and might even lead to scalp or skin irritations.


In our journey to achieve optimal hair health, understanding the science and benefits of products like leave-in conditioners is crucial. With insights from experts in the field, we’ve unveiled how these conditioners can be game-changers in our hair care routines. As we continue to prioritize our hair’s well-being, making informed choices will always lead us to shinier, healthier tresses.


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