How Scalp Treatments Work: The Hair Growth Cycle and Where Each Ingredient Acts
Scalp treatments are easier to judge once you understand the biology they are aimed at. Each hair on your head follows its own repeating cycle, and the ingredients used in prescription and over-the-counter products act at different points in that cycle. This guide explains the cycle, what changes in hereditary hair loss, and where the most common ingredients act. It is educational and does not replace medical advice.
The hair growth cycle in three phases
Growth (anagen). The follicle actively produces hair. This phase lasts for years, and most of the hairs on your scalp are in it at any one time.
Transition (catagen). Growth stops and the follicle shrinks. This lasts a few weeks.
Rest and shedding (telogen). The hair sits in the follicle for a few months and then falls out as a new one begins to grow beneath it.
Because each follicle runs on its own schedule, shedding some hair every day is normal.
What changes in hereditary hair loss
In pattern hair loss, follicles in certain areas of the scalp are sensitive to a hormone called DHT, which the body makes from testosterone. Over repeated cycles, affected follicles shrink. Their growth phase becomes shorter, and the hairs they produce become finer and shorter. This process is called miniaturization, and it happens gradually over years.
Other kinds of hair loss have different causes, and the ingredients below are not aimed at them.
Where each ingredient acts
Minoxidil
Where it acts. At the follicle and the small blood vessels around it. The exact way it works is not fully understood. It is thought to affect the growth phase of the cycle.
FDA status. Topical minoxidil is FDA-approved and sold over the counter for hereditary hair loss.
Worth knowing. Its labeling notes that a temporary increase in shedding can occur when starting, and that it needs to be used continuously.
Finasteride and dutasteride
Where they act. On the enzyme that converts testosterone into DHT. They are known as 5-alpha reductase inhibitors.
FDA status. Oral finasteride is FDA-approved for hair loss in men. Dutasteride is not FDA-approved for hair loss. No topical form of either is FDA-approved.
Worth knowing. The FDA issued an alert in 2025 about compounded topical finasteride, noting reports of side effects and the risk of exposure to others through skin contact. Women who are or may become pregnant should not use or handle these ingredients.
Ketoconazole
Where it acts. On the scalp surface. It is an antifungal that reduces a yeast associated with dandruff and scalp irritation.
FDA status. Approved in shampoo form for dandruff and related scalp conditions. It is not FDA-approved for hair loss.
Single ingredients and combination formulas
Some products contain one ingredient, and others combine several in a single application. Combination topical formulas are compounded by pharmacies for individual prescriptions. Compounded medications are not FDA-approved and have not been reviewed by the FDA for safety, effectiveness, or quality.
Nu Image prescribes two compounded topical preparations: NuDew®, a spray with minoxidil, ketoconazole, and finasteride, and NuDew Max®, a cream that also contains dutasteride. Both require evaluation by a licensed provider.
What scalp treatments cannot do
- Address every type of hair loss. Patchy loss, scarring conditions, and shedding caused by illness or stress need a different approach.
- Act on follicles that are no longer present. Where scarring has replaced follicles, topical products have nothing to act on.
- Work on a short schedule. The hair cycle is measured in months and years, so any assessment takes time and should be made with your provider.
- Replace a diagnosis. Thyroid problems, low iron, and scalp disease all need to be identified and treated directly.
Responses vary from person to person, and no product works for everyone.
Shampoos, oils, and supplements
Cosmetic products clean and condition the hair shaft and scalp surface. They do not act on the follicle's cycle. Hair supplements are not approved by the FDA and are not evaluated for effectiveness before sale.
Using a topical product safely
- Apply only as directed in your prescription
- Wash your hands after each application
- Let it dry before contact with other people, pillows, or shared towels
- Keep it away from pets, since minoxidil is toxic to cats and dogs
- Report scalp irritation, or any change in mood or sexual function, to your provider
Questions to ask a provider
- Which type of hair loss do I have?
- Which ingredients are in the product you recommend, and why?
- Is it FDA-approved or compounded?
- What side effects should I watch for?
- How and when will we review whether to continue?
Getting an evaluation
Nu Image offers online evaluations with licensed providers, who review your history and hair-loss pattern, decide whether a prescription is appropriate, and tell you when an in-person examination is the better route.
This content is for educational purposes only and is not medical advice, diagnosis, or treatment. NuDew® and NuDew Max® are compounded prescription preparations. Compounded medications are prepared by state-licensed compounding pharmacies and are not reviewed or approved by the FDA for safety, efficacy, or quality. Prescription products require an online consultation with a licensed healthcare provider, who will determine whether a prescription is appropriate.
This article is for informational purposes only and does not constitute medical advice. The information contained herein is not a substitute for and should never be relied upon for professional medical advice. Always talk to your physician about the risks and benefits of any treatment. Nu Image Medical may not offer the medications or services mentioned in this article.
