Many patients are surprised when alopecia areata appears as one or two bald patches while the rest of the scalp or beard looks completely normal. It often raises an important question:
If this is a hair loss condition, why does it not affect all the hair at once?
The answer lies in the biology of hair follicles and how the immune system behaves at a very local level.
Alopecia areata is a localized immune condition
Alopecia areata is an autoimmune disorder. The immune system mistakenly targets hair follicles, but it does not attack all follicles equally.
Only certain groups of follicles lose protection and become visible to the immune system. This is why hair loss appears in patches rather than across the entire scalp or beard.
Hair follicles have natural immune protection
Each hair follicle has a natural defense system called immune privilege. This system hides the follicle from immune attack and keeps inflammation low.
In alopecia areata, this protection collapses only in selected areas. Follicles just a few centimeters away may still be fully protected, allowing normal hair growth right next to bald patches.
The immune reaction stays confined
Once immune cells become active around a group of follicles, they release inflammatory signals that attract more immune cells to the same spot.
This creates a local inflammatory environment that stays confined to that area. Because this reaction does not spread evenly, hair loss remains patchy.
Hair growth cycles are different in each area
Not all hair follicles grow at the same time. Some are actively growing while others are resting.
Alopecia areata mainly affects follicles in the active growth phase called Anagen. When several nearby follicles are in this phase together, they become vulnerable at the same time, forming a visible patch.
Stress influences where patches appear
Hair follicles are closely connected to the nervous system. Stress signals can increase inflammation in specific areas of the scalp or beard.
This explains why alopecia areata often appears after emotional stress and why patches may develop in one region while other areas remain unaffected.
Genetics make some follicles more sensitive
Although alopecia areata has a genetic background, not all follicles behave the same way.
Some areas of the scalp or beard express higher immune activating signals, making them more prone to autoimmune attack. Other areas remain resistant.
What this means for patients?
Hair loss in alopecia areata is usually not permanent
The follicles are alive but temporarily inactive
Normal hair around bald patches is expected
Hair can regrow even after months of hair loss
The condition can improve, worsen, or move to different areas over time. This unpredictability is part of the disease process.
What this means for treatment?
Because alopecia areata is driven by immune imbalance, treatment focuses on calming inflammation and restoring follicle protection rather than only stimulating hair growth.
Early diagnosis and personalized treatment improve the chances of regrowth and long term control.
Why Alopecia Areata Can Progress to Alopecia Totalis or Universalis?
In some patients, alopecia areata does not remain localized. When immune activation becomes stronger and more persistent, the loss of immune protection can extend to most or all hair follicles. This leads to more extensive forms known as alopecia totalis, where the entire scalp is affected, or alopecia universalis, where body hair is also involved. These are not separate diseases, but more severe expressions of the same immune process, driven by higher genetic susceptibility, prolonged inflammation, and systemic immune triggers.
Cutiscity take home message
Alopecia areata causes patches because the immune system targets specific hair follicles, not the entire scalp. These follicles temporarily lose their immune protection, leading to localized hair loss while surrounding hair stays healthy.
Understanding this helps patients worry less and helps doctors choose treatments that address the real cause, not just the visible hair loss.
