Oily hair and oily skin why?
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causes of oily skin and oily hair sebaceous glands sebum overproduction
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Here is a thorough, textbook-backed explanation of why oily hair and oily skin occur.
Why Do You Get Oily Hair and Oily Skin?
Both come from the same source: sebaceous glands producing too much sebum.
What Are Sebaceous Glands?
Sebaceous glands are exocrine glands attached to hair follicles (together called the pilosebaceous unit). They exist almost everywhere on the skin - most densely on the scalp and face - which is exactly why those two areas get the oiliest. The glands secrete sebum into the space around the hair root, which then travels up the hair shaft and spreads onto the skin surface.
Sebum is not just "oil" - it is a mixture of:
- Wax esters and sterol esters
- Cholesterol
- Di- and triglycerides
- Squalene
- Vitamin E (an antioxidant)
In normal amounts, sebum protects skin from dehydration, free radicals, and environmental damage. Overproduction tips it into a problem - this is called seborrhea (or hyperseborrhea).
The Main Drivers of Oily Skin and Scalp
1. Androgens (Hormones) - The #1 Cause
This is the primary explanation. As confirmed by Dermatology 2-Volume Set 5e:
"Sebum production is controlled primarily by androgens... Androgen receptors, found in the basal layer of the sebaceous gland and the outer root sheath of the hair follicle, are responsive to testosterone and 5α-dihydrotestosterone (DHT), the most potent androgens. DHT has a 5- to 10-fold greater affinity than testosterone for the androgen receptor and is the principal androgen mediating sebum production."
- Puberty: Androgen levels surge, activating sebaceous glands - the main reason teenagers get oily skin and greasy hair.
- Adrenarche (around age 7-8): DHEAS from the adrenal gland begins rising, which is converted to active androgens inside sebaceous glands - this is why some kids develop oily skin even before full puberty.
- Decline with age: Sebum production tracks endogenous androgen production and typically falls off in the 7th-8th decade of life.
- In women, conditions that raise androgens (e.g. PCOS) cause notably oilier skin and scalp.
2. Genetics
Twin studies show identical twins have essentially the same sebum excretion rates, while non-identical twins differ significantly - confirming a strong genetic component to how active your sebaceous glands are. (Fitzpatrick's Dermatology)
3. Diet, Stress, and Exercise
All three influence hormone levels and therefore sebum output:
- High-glycaemic diets and dairy may increase insulin and IGF-1, which stimulate androgen activity.
- Stress raises cortisol and androgens (particularly DHEAS from the adrenal gland).
- Exercise transiently raises androgens.
4. Overwashing / Stripping the Skin
Paradoxically, washing hair or skin too aggressively strips away sebum, which can signal the glands to compensate by producing even more oil.
5. Heat and Humidity
Warm environments increase sebaceous gland activity and cause existing sebum to spread more readily over the skin and hair.
Why the Scalp and Face Are the Worst Affected
The scalp and face have the highest density of sebaceous glands in the body. Sebum travels up each hair shaft, so greasy hair is effectively greasy scalp oil coating the hair. The forehead, nose, and chin (T-zone) are similarly packed with glands.
Summary Table
| Factor | Effect on Oiliness |
|---|---|
| Androgens (DHT, testosterone, DHEAS) | Primary driver - stimulate sebocyte proliferation and sebum output |
| Genetics | Determines baseline gland activity |
| Puberty / hormonal changes | Major surge in sebum at adolescence |
| Stress | Raises adrenal androgens and cortisol |
| Diet (high GI, dairy) | Raises IGF-1/insulin -> more androgen activity |
| Hot/humid weather | Increases gland activity + spreads existing oil |
| Over-stripping skin/hair | Triggers compensatory overproduction |
Sources:
- Fitzpatrick's Dermatology, Sebum Production section
- Dermatology 2-Volume Set 5e, Hormonal Influences on Sebum Production
- DermNet NZ - Seborrhoea
- Healthline - What Is Sebum
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