AHA vs BHA vs PHA: The Complete Acid Decision Guide
AHA vs BHA vs PHA：果酸、水杨酸、PHA 完整决策指南
Key Takeaways
- AHA (glycolic, lactic, mandelic) = surface exfoliation, texture and tone. BHA (salicylic) = oil-soluble, dissolves clogs inside the pore. PHA (gluconolactone) = gentler AHA cousin for sensitive skin.
- Pick by concern: blackheads/oily → salicylic 2%; texture/dullness on tolerant skin → glycolic 8-10%; dry skin → lactic 10%; deeper skin tones with PIH → mandelic 8%; sensitive/rosacea → PHA 8%.
- Never layer two leave-on acids on the same night and never combine acids with retinoids on the same night. Use niacinamide on off-nights for barrier recovery.
- Salicylic acid does increase sun sensitivity — the 'BHA doesn't cause photosensitivity' claim is a myth. SPF 30+ daily with any acid.
- Start at 2 nights/week with PHA, escalate to target acid over 8 weeks. Frequency matters more than concentration for long-term results.
The three acid families, in one paragraph
AHAs (alpha hydroxy acids) are water-soluble acids that work on the skin surface — they loosen the bonds between dead corneocytes, accelerate desquamation, and stimulate collagen synthesis indirectly via mild inflammation signaling. The clinically validated members are glycolic acid, lactic acid, and mandelic acid. Concentration ranges: 5-10% for daily home use, 20-30% for once-weekly intensives, 30-70% for in-office peels.. Concentration ranges: 5-10% for daily home use, 20-30% for once-weekly intensives, 30-70% for in-office peels.
BHAs (beta hydroxy acids) are oil-soluble, which means they penetrate sebum-filled follicles and dissolve clogs from inside the pore — a fundamentally different mechanism from AHAs. The only cosmetic BHA you'll encounter is salicylic acid (and its precursor, willow bark). Concentration ranges: 0.5-2% for daily leave-on, up to 30% for in-office peels. (and its precursor, willow bark). Concentration ranges: 0.5-2% for daily leave-on, up to 30% for in-office peels.
PHAs (polyhydroxy acids) are larger-molecule cousins of AHAs — most commonly gluconolactone and lactobionic acid. The larger molecule penetrates more slowly, which means less irritation and better tolerance for sensitive or rosacea-prone skin, at the cost of slower visible results. Concentration ranges: 4-10% for daily use; PHAs are rarely used in peels because the milder action defeats the purpose. and lactobionic acid. The larger molecule penetrates more slowly, which means less irritation and better tolerance for sensitive or rosacea-prone skin, at the cost of slower visible results. Concentration ranges: 4-10% for daily use; PHAs are rarely used in peels because the milder action defeats the purpose.
A 2015 review in *Molecules* (Tang & Yang) summarized the irritation hierarchy as glycolic > lactic > mandelic > salicylic > gluconolactone, which roughly inverts the molecule-size hierarchy — smaller molecule, deeper penetration, more bite.A 2015 review in *Molecules* (Tang & Yang) summarized the irritation hierarchy as glycolic > lactic > mandelic > salicylic > gluconolactone, which roughly inverts the molecule-size hierarchy — smaller molecule, deeper penetration, more bite.
中文翻译 · 三大酸家族，一段说清
AHA（α-羟基酸）是水溶性酸，作用在皮肤表面——松动角质细胞间的连接、加速脱屑，并通过轻度炎症信号间接刺激胶原合成。临床验证的成员包括甘醇酸、乳酸、扁桃酸。浓度范围：家用每日 5-10%，每周强效 20-30%，院线刷酸 30-70%。。浓度范围：家用每日 5-10%，每周强效 20-30%，院线刷酸 30-70%。
BHA（β-羟基酸）是脂溶性，能渗入充满皮脂的毛囊从内部溶解堵塞——与 AHA 完全不同的机制。化妆品中唯一的 BHA 是水杨酸（及其前体柳树皮）。浓度范围：日用留涂 0.5-2%，院线刷酸最高 30%。（及其前体柳树皮）。浓度范围：日用留涂 0.5-2%，院线刷酸最高 30%。
PHA（多羟基酸）是 AHA 的大分子表亲——最常见的是葡糖酸内酯和乳糖酸。大分子渗透更慢，意味着刺激更少、敏感肌和玫瑰痤疮倾向者更耐受，代价是见效更慢。浓度范围：日用 4-10%；PHA 很少用于刷酸，因为太温和达不到目的。和乳糖酸。大分子渗透更慢，意味着刺激更少、敏感肌和玫瑰痤疮倾向者更耐受，代价是见效更慢。浓度范围：日用 4-10%；PHA 很少用于刷酸，因为太温和达不到目的。
2015 年 *Molecules* 综述（Tang & Yang）总结刺激度排序：甘醇酸 > 乳酸 > 扁桃酸 > 水杨酸 > 葡糖酸内酯——基本与分子大小成反比，分子越小渗透越深，刺激越大。2015 年 *Molecules* 综述（Tang & Yang）总结刺激度排序：甘醇酸 > 乳酸 > 扁桃酸 > 水杨酸 > 葡糖酸内酯——基本与分子大小成反比，分子越小渗透越深，刺激越大。
The five acids, individually
[Glycolic acid](/ingredients/glycolic-acid) — the smallest AHA (molecular weight 76 Da), derived from sugar cane. Penetrates fastest, works fastest, irritates most. Best for: texture, dullness, fine lines, photodamage on tolerant skin. Concentration: start at 5%, work up to 10%. A 1996 Ditre et al. study in *J Am Acad Dermatol* showed 25% glycolic for 6 months thickened the epidermis 25% and increased collagen — the foundational AHA study everyone cites. — the smallest AHA (molecular weight 76 Da), derived from sugar cane. Penetrates fastest, works fastest, irritates most. Best for: texture, dullness, fine lines, photodamage on tolerant skin. Concentration: start at 5%, work up to 10%. A 1996 Ditre et al. study in *J Am Acad Dermatol* showed 25% glycolic for 6 months thickened the epidermis 25% and increased collagen — the foundational AHA study everyone cites.
[Lactic acid](/ingredients/lactic-acid) — slightly larger (90 Da), derived from milk fermentation. Doubles as a humectant (it's part of the skin's natural moisturizing factor). Gentler than glycolic at equivalent concentration. Best for: dry skin needing exfoliation, mild brightening, hyperpigmentation. Concentration: 5-12% leave-on. The 1996 Smith study compared 12% lactic to 12% glycolic and found similar efficacy with less irritation from lactic. — slightly larger (90 Da), derived from milk fermentation. Doubles as a humectant (it's part of the skin's natural moisturizing factor). Gentler than glycolic at equivalent concentration. Best for: dry skin needing exfoliation, mild brightening, hyperpigmentation. Concentration: 5-12% leave-on. The 1996 Smith study compared 12% lactic to 12% glycolic and found similar efficacy with less irritation from lactic.
[Mandelic acid](/ingredients/mandelic-acid) — much larger (152 Da), derived from bitter almonds. Penetrates slowly and evenly, with mild antibacterial activity that makes it useful for acne-prone skin. Best for: acne + hyperpigmentation in deeper skin tones (lower risk of post-inflammatory darkening than glycolic). Concentration: 5-10% leave-on, 30-50% in-office peels. The 2009 Sarkar study on Indian patients showed mandelic was the safest peel option for Fitzpatrick IV-VI. — much larger (152 Da), derived from bitter almonds. Penetrates slowly and evenly, with mild antibacterial activity that makes it useful for acne-prone skin. Best for: acne + hyperpigmentation in deeper skin tones (lower risk of post-inflammatory darkening than glycolic). Concentration: 5-10% leave-on, 30-50% in-office peels. The 2009 Sarkar study on Indian patients showed mandelic was the safest peel option for Fitzpatrick IV-VI.
[Salicylic acid](/ingredients/salicylic-acid) — 138 Da, oil-soluble, the only BHA you'll meet. Goes through sebum into the follicle. Best for: blackheads, whiteheads, oily skin, mild acne, congested pores, fungal acne (it's anti-inflammatory and mildly antimicrobial). Concentration: 0.5% in wash-off cleansers, 1-2% in leave-on serums, 5-10% in spot treatments, 20-30% in clinic peels. The Kligman protocol used 30% salicylic peels for cystic acne to outstanding effect. — 138 Da, oil-soluble, the only BHA you'll meet. Goes through sebum into the follicle. Best for: blackheads, whiteheads, oily skin, mild acne, congested pores, fungal acne (it's anti-inflammatory and mildly antimicrobial). Concentration: 0.5% in wash-off cleansers, 1-2% in leave-on serums, 5-10% in spot treatments, 20-30% in clinic peels. The Kligman protocol used 30% salicylic peels for cystic acne to outstanding effect.
[Gluconolactone (PHA)](/ingredients/pha-gluconolactone) — 178 Da, the kindest acid on this list. Doubles as a humectant and a mild antioxidant. Best for: sensitive skin, rosacea, post-procedure recovery, anyone whose skin can't tolerate AHAs. Concentration: 4-10% leave-on. The Edison & Green 2004 study in *Cutis* validated PHA tolerance in rosacea patients who had failed glycolic and lactic. — 178 Da, the kindest acid on this list. Doubles as a humectant and a mild antioxidant. Best for: sensitive skin, rosacea, post-procedure recovery, anyone whose skin can't tolerate AHAs. Concentration: 4-10% leave-on. The Edison & Green 2004 study in *Cutis* validated PHA tolerance in rosacea patients who had failed glycolic and lactic.
中文翻译 · 五种酸的逐一拆解
[甘醇酸](/ingredients/glycolic-acid) — 最小的 AHA（分子量 76 Da），源自甘蔗。渗透最快，见效最快，刺激最大。适合：质地粗糙、暗沉、细纹、光老化（耐受型肌肤）。浓度：5% 起步，逐步到 10%。1996 年 Ditre 等在 *J Am Acad Dermatol* 的研究显示，25% 甘醇酸用 6 个月可使表皮增厚 25% 并增加胶原——所有人都引用的基础研究。 — 最小的 AHA（分子量 76 Da），源自甘蔗。渗透最快，见效最快，刺激最大。适合：质地粗糙、暗沉、细纹、光老化（耐受型肌肤）。浓度：5% 起步，逐步到 10%。1996 年 Ditre 等在 *J Am Acad Dermatol* 的研究显示，25% 甘醇酸用 6 个月可使表皮增厚 25% 并增加胶原——所有人都引用的基础研究。
[乳酸](/ingredients/lactic-acid) — 稍大（90 Da），源自牛奶发酵。兼具保湿功能（它是皮肤天然保湿因子的一部分）。同浓度下比甘醇酸温和。适合：干性肌需要去角质、轻度提亮、色沉。浓度：5-12% 留涂。1996 年 Smith 研究对比 12% 乳酸与 12% 甘醇酸，效果相近但乳酸刺激更小。 — 稍大（90 Da），源自牛奶发酵。兼具保湿功能（它是皮肤天然保湿因子的一部分）。同浓度下比甘醇酸温和。适合：干性肌需要去角质、轻度提亮、色沉。浓度：5-12% 留涂。1996 年 Smith 研究对比 12% 乳酸与 12% 甘醇酸，效果相近但乳酸刺激更小。
[扁桃酸](/ingredients/mandelic-acid) — 大得多（152 Da），源自苦杏仁。渗透慢而均匀，有轻度抗菌作用，适合痘痘肌。适合：深色肤的痘痘 + 色沉（炎症后色沉风险低于甘醇酸）。浓度：留涂 5-10%，院线刷酸 30-50%。2009 年 Sarkar 对印度患者的研究显示，扁桃酸是 Fitzpatrick IV-VI 最安全的换肤选择。 — 大得多（152 Da），源自苦杏仁。渗透慢而均匀，有轻度抗菌作用，适合痘痘肌。适合：深色肤的痘痘 + 色沉（炎症后色沉风险低于甘醇酸）。浓度：留涂 5-10%，院线刷酸 30-50%。2009 年 Sarkar 对印度患者的研究显示，扁桃酸是 Fitzpatrick IV-VI 最安全的换肤选择。
[水杨酸](/ingredients/salicylic-acid) — 138 Da，脂溶，唯一的 BHA。能穿透皮脂进入毛囊。适合：黑头、白头、油皮、轻度痤疮、毛孔堵塞、马拉色菌毛囊炎（抗炎 + 轻度抗菌）。浓度：洁面 0.5%，留涂精华 1-2%，点涂 5-10%，院线刷酸 20-30%。Kligman 经典方案对囊肿型痤疮用 30% 水杨酸刷酸，效果惊人。 — 138 Da，脂溶，唯一的 BHA。能穿透皮脂进入毛囊。适合：黑头、白头、油皮、轻度痤疮、毛孔堵塞、马拉色菌毛囊炎（抗炎 + 轻度抗菌）。浓度：洁面 0.5%，留涂精华 1-2%，点涂 5-10%，院线刷酸 20-30%。Kligman 经典方案对囊肿型痤疮用 30% 水杨酸刷酸，效果惊人。
[葡糖酸内酯（PHA）](/ingredients/pha-gluconolactone) — 178 Da，本列表最温和的酸。兼具保湿和轻度抗氧化。适合：敏感肌、玫瑰痤疮、术后修复、不耐受 AHA 的所有人。浓度：留涂 4-10%。2004 年 Edison & Green 在 *Cutis* 验证了 PHA 对甘醇酸和乳酸都不耐受的玫瑰痤疮患者的耐受性。 — 178 Da，本列表最温和的酸。兼具保湿和轻度抗氧化。适合：敏感肌、玫瑰痤疮、术后修复、不耐受 AHA 的所有人。浓度：留涂 4-10%。2004 年 Edison & Green 在 *Cutis* 验证了 PHA 对甘醇酸和乳酸都不耐受的玫瑰痤疮患者的耐受性。
The decision matrix — pick by concern, not by hype
Skip the brand recommendations on TikTok. Pick by what you're actually trying to fix:Skip the brand recommendations on TikTok. Pick by what you're actually trying to fix:
Blackheads, whiteheads, oily T-zone, congested pores → salicylic acid 2%, leave-on, nightly. BHAs go into the pore; AHAs don't. There is no AHA substitute for this concern. 2%, leave-on, nightly. BHAs go into the pore; AHAs don't. There is no AHA substitute for this concern.
Rough texture, dullness, fine lines on tolerant skin → glycolic acid 8-10% leave-on, 2-3x weekly. Strongest re-surfacing effect of the daily-use acids. 8-10% leave-on, 2-3x weekly. Strongest re-surfacing effect of the daily-use acids.
Dry skin with mild dullness or KP-style bumps → lactic acid 10-12% leave-on, 2-3x weekly. Doubles as a humectant so it doesn't dry the skin further. 10-12% leave-on, 2-3x weekly. Doubles as a humectant so it doesn't dry the skin further.
Acne + post-inflammatory hyperpigmentation on Fitzpatrick IV-VI → mandelic acid 8-10% leave-on, 3-5x weekly. Lowest risk of darkening the very marks you're trying to fade. Often combined with azelaic acid 10%. 10%.
Sensitive skin, rosacea, eczema-prone, post-procedure → PHA gluconolactone 8-10% leave-on, nightly. The only acid most rosacea patients can use without flushing. 8-10% leave-on, nightly. The only acid most rosacea patients can use without flushing.
Body — KP (keratosis pilaris), back acne, rough elbows → glycolic 10-15% or lactic acid 12% body lotion, daily. The body tolerates higher concentrations than the face. 12% body lotion, daily. The body tolerates higher concentrations than the face.
You don't know your skin yet → start with PHA. Add an AHA or BHA only after you've used PHA for 4 weeks without any irritation. → start with PHA. Add an AHA or BHA only after you've used PHA for 4 weeks without any irritation.
中文翻译 · 决策矩阵——按诉求选，不按热度选
别看 TikTok 的品牌推荐。按你真正要解决的问题选：别看 TikTok 的品牌推荐。按你真正要解决的问题选：
黑头、白头、T 区油、毛孔堵塞 → 水杨酸 2% 留涂，每晚。BHA 才能进毛孔，AHA 不行，没有 AHA 能替代。 2% 留涂，每晚。BHA 才能进毛孔，AHA 不行，没有 AHA 能替代。
质地粗糙、暗沉、细纹（耐受肌） → 甘醇酸 8-10% 留涂，每周 2-3 次。日用酸中重塑表皮最强。 8-10% 留涂，每周 2-3 次。日用酸中重塑表皮最强。
干皮 + 轻度暗沉或鸡皮疙瘩 → 乳酸 10-12% 留涂，每周 2-3 次。兼具保湿不会进一步干燥。 10-12% 留涂，每周 2-3 次。兼具保湿不会进一步干燥。
Fitzpatrick IV-VI 痘痘 + 痘印 → 扁桃酸 8-10% 留涂，每周 3-5 次。最不容易把要淡化的痘印变深。常与 杜鹃花酸 10% 联用。 10% 联用。
敏感肌、玫瑰痤疮、湿疹倾向、术后 → PHA 葡糖酸内酯 8-10% 留涂，每晚。多数玫瑰痤疮患者唯一能不潮红的酸。 8-10% 留涂，每晚。多数玫瑰痤疮患者唯一能不潮红的酸。
身体——鸡皮、背痘、粗糙肘部 → 甘醇酸 10-15% 或 乳酸 12% 身体乳，每天。身体耐受度比脸高得多。 12% 身体乳，每天。身体耐受度比脸高得多。
完全不了解自己的肌肤 → 从 PHA 起步。用 PHA 4 周无任何刺激后，再加 AHA 或 BHA。 → 从 PHA 起步。用 PHA 4 周无任何刺激后，再加 AHA 或 BHA。
Layering rules and common mistakes
Never layer two leave-on acids at once. Glycolic + salicylic at full strength on the same night is how people get chemical burns. If you want both effects, alternate nights (AHA Mon-Wed-Fri, BHA Tue-Thu-Sat, rest Sunday) or use a pre-formulated combo at moderate concentrations (Paula's Choice 25% AHA + 2% BHA is a once-weekly intensive, not a nightly). Glycolic + salicylic at full strength on the same night is how people get chemical burns. If you want both effects, alternate nights (AHA Mon-Wed-Fri, BHA Tue-Thu-Sat, rest Sunday) or use a pre-formulated combo at moderate concentrations (Paula's Choice 25% AHA + 2% BHA is a once-weekly intensive, not a nightly).
Never layer acids with retinoids on the same night. Retinoids already exfoliate via the receptor pathway. Adding an acid is double-dosing the irritation. Pattern: retinoid 3 nights, acid 2 nights, rest 2 nights. Retinoids already exfoliate via the receptor pathway. Adding an acid is double-dosing the irritation. Pattern: retinoid 3 nights, acid 2 nights, rest 2 nights.
Always use [niacinamide](/ingredients/niacinamide) on off-nights. Niacinamide repairs the barrier the acids strip. It is not a competitor active — it's the recovery partner that lets you tolerate more frequent acid use. Niacinamide repairs the barrier the acids strip. It is not a competitor active — it's the recovery partner that lets you tolerate more frequent acid use.
Always apply SPF daily, no exception. Every acid in this article thins the stratum corneum and increases UV sensitivity for at least 7 days post-use, salicylic acid included (despite the persistent myth that 'BHA doesn't increase sun sensitivity'). A 2002 Kornhauser study quantified the UVB sensitivity bump at about 1.5-2x baseline after 4 weeks of AHA use. Every acid in this article thins the stratum corneum and increases UV sensitivity for at least 7 days post-use, salicylic acid included (despite the persistent myth that 'BHA doesn't increase sun sensitivity'). A 2002 Kornhauser study quantified the UVB sensitivity bump at about 1.5-2x baseline after 4 weeks of AHA use.
Don't use acids on broken or compromised skin. Active eczema, sunburn, recent retinoid burn, freshly waxed or threaded skin — pause acids for 7-14 days. Active eczema, sunburn, recent retinoid burn, freshly waxed or threaded skin — pause acids for 7-14 days.
Don't stack acids with physical exfoliants. A glycolic toner plus a scrub plus a konjac sponge is how people destroy their barrier in a week. Pick one method. is how people destroy their barrier in a week. Pick one method.
中文翻译 · 叠加规则与常见错误
绝对不要同一晚叠加两种留涂酸。 全浓度甘醇酸 + 水杨酸同晚使用是化学灼伤的标配方式。如果想要双重效果，分晚交替（AHA 周一三五，BHA 周二四六，周日休）；或者用预配好的中浓度复合产品（Paula's Choice 25% AHA + 2% BHA 是每周一次的强效，不是每晚）。 全浓度甘醇酸 + 水杨酸同晚使用是化学灼伤的标配方式。如果想要双重效果，分晚交替（AHA 周一三五，BHA 周二四六，周日休）；或者用预配好的中浓度复合产品（Paula's Choice 25% AHA + 2% BHA 是每周一次的强效，不是每晚）。
绝对不要同一晚叠加酸和 A 醇。 A 醇本身通过受体通路就在去角质。再加酸就是双倍刺激。模式：A 醇 3 晚，酸 2 晚，休 2 晚。 A 醇本身通过受体通路就在去角质。再加酸就是双倍刺激。模式：A 醇 3 晚，酸 2 晚，休 2 晚。
休息夜永远用[烟酰胺](/ingredients/niacinamide)。 烟酰胺修复酸剥离的屏障。它不是竞争活性，是让你能更频繁用酸的修复搭档。 烟酰胺修复酸剥离的屏障。它不是竞争活性，是让你能更频繁用酸的修复搭档。
每天必硬防晒，无例外。 本文每种酸都会薄化角质层、增加 UV 敏感性至少 7 天，包括水杨酸（尽管「BHA 不增加光敏」的传言流传甚广）。2002 年 Kornhauser 研究量化：用 AHA 4 周后 UVB 敏感度上升约 1.5-2 倍。（尽管「BHA 不增加光敏」的传言流传甚广）。2002 年 Kornhauser 研究量化：用 AHA 4 周后 UVB 敏感度上升约 1.5-2 倍。
屏障受损或破皮时不要用酸。 急性湿疹、晒伤、A 醇灼伤、刚做完热蜡或线脱毛——停酸 7-14 天。 急性湿疹、晒伤、A 醇灼伤、刚做完热蜡或线脱毛——停酸 7-14 天。
不要叠加物理去角质。 甘醇酸爽肤水 + 磨砂膏 + 蒟蒻海绵 = 一周毁屏障。三选一。 甘醇酸爽肤水 + 磨砂膏 + 蒟蒻海绵 = 一周毁屏障。三选一。
The progression plan — how to introduce acids safely
Weeks 1-2. Start with PHA gluconolactone 8% leave-on, 2 nights per week. Apply on dry skin after cleansing, wait 10 minutes, then moisturizer. Watch for any redness, tightness, or stinging beyond 30 seconds — that's your tolerance signal. Start with PHA gluconolactone 8% leave-on, 2 nights per week. Apply on dry skin after cleansing, wait 10 minutes, then moisturizer. Watch for any redness, tightness, or stinging beyond 30 seconds — that's your tolerance signal.
Weeks 3-4. If PHA caused zero irritation, increase to every other night. Add a gentle barrier repair product (ceramide cream) on off-nights. If PHA caused zero irritation, increase to every other night. Add a gentle barrier repair product (ceramide cream) on off-nights.
Weeks 5-8. Graduate to your target acid. If you tolerated PHA, you can move to lactic 8-10% or mandelic 8% on the same every-other-night schedule. Stronger acids (glycolic 10%, salicylic 2% leave-on) should still be 3 nights/week max for the first month. Graduate to your target acid. If you tolerated PHA, you can move to lactic 8-10% or mandelic 8% on the same every-other-night schedule. Stronger acids (glycolic 10%, salicylic 2% leave-on) should still be 3 nights/week max for the first month.
Weeks 9-12. Build to maintenance. Most adults end up at one of three patterns: (a) salicylic 2% nightly for oily/acne skin, (b) glycolic 8% every other night for texture/anti-aging, (c) PHA nightly for sensitive skin. AHA and BHA can be alternated for combination skin (BHA on the T-zone, AHA on cheeks). Build to maintenance. Most adults end up at one of three patterns: (a) salicylic 2% nightly for oily/acne skin, (b) glycolic 8% every other night for texture/anti-aging, (c) PHA nightly for sensitive skin. AHA and BHA can be alternated for combination skin (BHA on the T-zone, AHA on cheeks).
Maintenance forever. Acids work because of consistent low-dose use. Five years of 2% salicylic 5 nights/week beats a single 30% peel for long-term pore size and skin clarity. The trap is escalating concentration looking for faster results — escalating frequency of barrier repair is the safer lever. Acids work because of consistent low-dose use. Five years of 2% salicylic 5 nights/week beats a single 30% peel for long-term pore size and skin clarity. The trap is escalating concentration looking for faster results — escalating frequency of barrier repair is the safer lever.
中文翻译 · 渐进方案——如何安全引入酸类
第 1-2 周。 从 PHA 葡糖酸内酯 8% 留涂起步，每周 2 晚。洁面后干肌使用，等 10 分钟后保湿。观察是否出现红、紧、刺痛超过 30 秒——那是你的耐受信号。 从 PHA 葡糖酸内酯 8% 留涂起步，每周 2 晚。洁面后干肌使用，等 10 分钟后保湿。观察是否出现红、紧、刺痛超过 30 秒——那是你的耐受信号。
第 3-4 周。 如果 PHA 完全无刺激，提到隔晚一次。休息夜加温和屏障修复（神经酰胺面霜）。 如果 PHA 完全无刺激，提到隔晚一次。休息夜加温和屏障修复（神经酰胺面霜）。
第 5-8 周。 升级到目标酸。如果耐受 PHA，可以转到乳酸 8-10% 或扁桃酸 8% 维持隔晚一次。更强的酸（甘醇酸 10%、水杨酸 2% 留涂）头一个月最多每周 3 晚。 升级到目标酸。如果耐受 PHA，可以转到乳酸 8-10% 或扁桃酸 8% 维持隔晚一次。更强的酸（甘醇酸 10%、水杨酸 2% 留涂）头一个月最多每周 3 晚。
第 9-12 周。 建立维持方案。多数成年人会落到三种模式之一：(a) 油痘肌每晚 2% 水杨酸，(b) 抗老 / 质地隔晚 8% 甘醇酸，(c) 敏感肌每晚 PHA。混合肌可分区交替（T 区 BHA，脸颊 AHA）。 建立维持方案。多数成年人会落到三种模式之一：(a) 油痘肌每晚 2% 水杨酸，(b) 抗老 / 质地隔晚 8% 甘醇酸，(c) 敏感肌每晚 PHA。混合肌可分区交替（T 区 BHA，脸颊 AHA）。
永久维持。 酸有效是因为长期低剂量。5 年 2% 水杨酸每周 5 晚远胜单次 30% 刷酸的长期效果。陷阱是为了加快效果不断升级浓度——升级屏障修复频率才是更安全的杠杆。 酸有效是因为长期低剂量。5 年 2% 水杨酸每周 5 晚远胜单次 30% 刷酸的长期效果。陷阱是为了加快效果不断升级浓度——升级屏障修复频率才是更安全的杠杆。
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Frequently Asked Questions
What is the difference between AHA and BHA?
AHAs (glycolic, lactic, mandelic) are water-soluble and work on the surface, loosening dead skin cells and stimulating collagen. BHAs (salicylic acid) are oil-soluble and penetrate sebum-filled follicles to dissolve clogs from inside the pore. Use AHA for texture, dullness, and fine lines; use BHA for blackheads, whiteheads, and oily skin.
Can I use AHA and BHA together?
Yes, but not at full strength on the same night. Best options: (1) alternate nights — AHA Mon/Wed/Fri, BHA Tue/Thu/Sat, rest Sunday, or (2) use a pre-formulated combination product designed for the layered exposure (e.g., Paula's Choice 25% AHA + 2% BHA Exfoliant once weekly as an intensive). Same-night layering of two leave-on acids at full strength is the most common cause of acid-induced chemical burns.
What is PHA gluconolactone and is it better than AHA?
PHA (polyhydroxy acid) — most commonly gluconolactone — is a larger-molecule cousin of AHA. The larger molecule penetrates more slowly, causing less irritation than glycolic or lactic acid. It is not 'better' — it is gentler. PHA is the right choice for sensitive skin, rosacea, post-procedure recovery, or anyone whose skin can't tolerate AHAs. For tolerant skin focused on faster results, AHA is still the more efficient choice.
Which acid is best for dark skin?
Mandelic acid (5-10% leave-on) and azelaic acid (10-20%). Both have a much lower risk of post-inflammatory hyperpigmentation than glycolic acid in Fitzpatrick IV-VI skin tones. A 2009 Sarkar study on Indian patients showed mandelic was the safest peel option for darker skin. Glycolic acid at high concentrations can paradoxically darken the very pigmentation it's meant to fade.
Does salicylic acid increase sun sensitivity?
Yes — despite the persistent myth that 'only AHAs cause sun sensitivity.' All exfoliating acids thin the stratum corneum and increase UV penetration for at least 7 days after use. Always wear SPF 30+ daily when using any acid, including salicylic. A 2002 Kornhauser study found AHA use roughly doubles UVB-induced erythema sensitivity after 4 weeks.
How often should I use glycolic acid?
Start at 2 nights per week with 5-7% concentration. Increase to every other night by week 4 if tolerated. Most adults stabilize at 3-4 nights per week with 8-10% glycolic for texture and anti-aging use, or once weekly at 20-30% as an intensive. Going beyond 4 nights per week rarely adds benefit and frequently strips the barrier.
Can I use acids while pregnant?
Low-concentration AHAs (glycolic and lactic under 10%) are generally considered safe during pregnancy as systemic absorption is minimal. PHA gluconolactone is also safe. Salicylic acid is acceptable at 2% in wash-off cleansers per ACOG, but leave-on serums above 2% should be avoided due to systemic absorption similar to oral aspirin. When in doubt, switch to azelaic acid, which is the most pregnancy-safe exfoliating-adjacent active available.
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AI-assisted, human-reviewed. Educational content only; not medical advice. Consult your dermatologist or obstetrician for personal medical questions.