What areas of the body are considered terminal hair bearing areas?

Terminal Hair Bearing Areas of the Body

Terminal hair bearing areas include the scalp, pubic region, axillary (armpit) regions, and beard area in men. These areas are specifically identified in dermatology guidelines as regions where terminal hair grows naturally 1.

What Makes an Area Terminal Hair Bearing

Terminal hair differs from vellus hair in several important characteristics:

• Size: Terminal hairs are larger, thicker, and more pigmented than vellus hairs 2, 3
• Follicle depth: Terminal hair follicles penetrate deeper below the skin surface (3.52 mm vs. 2.59 mm for intermediate hairs) 2
• Structure: Terminal hair follicles have larger:
  • Hair fiber diameter (0.07 mm vs. 0.03 mm)
  • Connective tissue sheath (0.33 mm vs. 0.24 mm)
  • Bulb (0.31 mm vs. 0.19 mm)
  • Dermal papilla (0.12 mm vs. 0.06 mm) 2

Clinical Significance of Terminal Hair Bearing Areas

The identification of terminal hair bearing areas is clinically important for several reasons:

1. Treatment Considerations for Skin Cancers

Both basal cell carcinoma (BCC) and cutaneous squamous cell carcinoma (cSCC) guidelines specifically mention terminal hair bearing areas as regions where certain treatments should be avoided:

• Curettage and electrodesiccation (C&E) is considered less effective in terminal hair bearing areas because of potential follicular extension of tumor 1
• The NCCN guidelines specifically state: "For lesions on terminal hair-bearing skin (scalp, pubic, axillary regions, and beard area in men), C&E is considered less effective because of potential follicular extension of tumor" 1

2. Androgen Effects on Terminal Hair

Terminal hair bearing areas respond differently to androgens:

• After puberty, androgens promote transformation of vellus follicles to terminal ones in areas like the axilla 4
• In men, androgens promote terminal hair growth in the beard area 4
• Paradoxically, androgens can cause the opposite transformation on the scalp, leading to androgenetic alopecia 4

Diagnostic Applications

Understanding terminal hair distribution is important for:

• Hirsutism assessment: Excess terminal hair growth in women in a male-like pattern is evaluated using scoring systems like the modified Ferriman-Gallwey (mFG) score 5, 6
• Simplified scoring systems for hirsutism focus on specific terminal hair bearing areas including upper lip, lower back, lower abdomen, and thigh 6

Key Considerations for Clinicians

When treating skin conditions in terminal hair bearing areas:

1. For skin cancers: Avoid C&E in these regions; instead, consider standard excision, Mohs micrographic surgery, or radiation therapy for non-surgical candidates 1

2. For hair removal procedures: Terminal hair requires different treatment parameters than vellus hair due to deeper follicles and larger structures 2, 3

3. For drug delivery: The morphometric differences between terminal and vellus hair follicles affect drug delivery systems targeting hair follicles 3

Terminal hair bearing areas represent distinct anatomical regions with unique characteristics that must be considered in dermatological practice, particularly when treating skin cancers and other conditions requiring specialized approaches.