Table 3.

Summary table of key points for rapid differential diagnosis of common non-scarring alopecia.

	Clinical Presentation	Histopathological Findings	Related Genes
FPHL	Widening of the central part line Preservation of the hairline shape Miniaturization of hair follicles Increased hair shedding (not always present)	Increased number of miniaturized hair follicles, a terminal to vellus ratio (T/V ratio) usually less than 2:1 Reduced size of sebaceous glands Decreased anagen to telogen ratio Increased number of follicular stelae Perifollicular inflammation around the upper portion of the hair follicle with or without perifollicular fibrosis	CYP19A1 ESR2
M-AGA	Gradual hair thinning in a distinct pattern (typically at the temples and crown) Miniaturization of hair follicles leading to finer, shorter hairs Increased hair shedding, especially during washing or brushing		AR MC4R EDA2R SRD5A1 SRD5A2 [2,47]
Alopecia areata	Patchy hair loss in round or oval-shaped areas Hair loss can progress to involve the entire scalp (alopecia totalis) or the entire body (alopecia universalis)	“Swarm of Bees” pattern Peribulbar lymphocytic inflammation Catagen/telogen arrest Follicular miniaturization Exclamation mark hairs Dystrophic anagen hairs	NOTCH4 C6orf10 BTNL2 HLA-DRA HLA-A IL-2 IL2RA STX17 TNXB [71,72]
Chronic Telogen effluvium	Excessive shedding of telogen (resting) hairs for more than six months Generalized thinning of hair all over the scalp without visible bald patches or specific pattern Hair regrowth usually occurs once the underlying cause is addressed	Increased number of telogen hairs No peribulbar inflammation Preserved follicular structure Absence of miniaturization	Cdx1 VDR Taq1 VDR [73]