Rudolph Care Sun Face Serum SPF 30

DHHB has been approved by the EU, Japan, Taiwan, and South America for use up to 10%. Unfortunately, it has not been approved for use in the US or Canada due to slow regulatory processes.

This ingredient is soluble in oils, fats, and lipids.

Your skin makes glycerin on its own (mostly from sebaceous oil breakdown) and shuttles it to your outermost layer of skin, or your epidermis, via aquaporin-3.

Aquaporin-3 is a transporter that is essential for normal skin hydration, elasticity, and repair. Interestingly, mice lacking in AQP3 have dry and less elastic skin that can be fully corrected with glycerin.

This ingredient is non-irritating, plays well with almost every ingredient, and works across all skin types. Typical use is anywhere between 3-10% but can go up to 79% in some leave-on products.

Just know very high concentrations (>40%) can feel tacky in low humidity.

Glycerin is the name for this ingredient in American English. British English uses Glycerol/Glycerine.

Ethylhexyl Triazone is oil soluble, oderless and colorless, which mean it is able to be incorporated into a variety of different formulations.

It is not currently available within the United States due to slow changing FDA regulations. Outside of the US, it is used in formulations at concentrations up to 5%.

You'll also recognize water as that liquid we all need to stay alive. If you see this, drink a glass of water. Remember to stay hydrated!

You might have heard of "niacin flush", or the reddening of skin that causes itchiness. Niacinamide has not been found to cause this.

In very rare cases, some individuals may not be able to tolerate niacinamide at all or experience an allergic reaction to it.

If you are experiencing flaking, irritation, and dryness with this ingredient, be sure to double check all your products as this ingredient can be found in all categories of skincare.

When incorporating niacinamide into your routine, look out for concentration amounts. Typically, 5% niacinamide provides benefits such as fading dark spots. However, if you have sensitive skin, it is better to begin with a smaller concentration.

When you apply niacinamide to your skin, your body converts it into nicotinamide adenine dinucleotide (NAD). NAD is an essential coenzyme that is already found in your cells as "fuel" and powers countless biological processes.

In your skin, NAD helps repair cell damage, produce new healthy cells, support collagen production, strengthen the skin barrier, and fight environmental stressors (like UV and pollution).

Our natural NAD levels start to decline with age, leading to slower skin repair, visible aging, and a weaker skin barrier. By providing your skin niacinamide, you're recharging your skin's NAD levels. This leads to stronger, healthier, and younger looking skin.

Another name for vitamin B3 is nicotinamide. This vitamin is water-soluble and our bodies don't store it. We obtain Vitamin B3 from either food or skincare. Meat, fish, wheat, yeast, and leafy greens contain vitamin B3.

The type of niacinamide used in skincare is synthetically created.

It is also pretty water-resistant and is highly oil-soluble (so your oil cleanser will get it off right away).

This ingredient is currently available in Europe and Japan, but not in the US.

Another pro?

It's exceptionally photostable, barely degrades in sunlight, and acts as a "bodyguard" for less stable filters.

That's why you'll see it paired with avobenzone or octinoxate; this team up ensures they keep working through sun exposure.

Safety reviews have been reassuring across the board. This ingredient shows low absorption through the skin, rarely irritates, and lab studies found it doesn't act like a hormone in the body (a concern that's been raised about some older sunscreen filters).

On maximum concentrations:

In 2026, the US F.D.A finally added it as an OTC sunscreen ingredient at concentrations up to 6% for adults / children 6 months and older

Studies show inulin may help with controlling your skin's natural microbiota when applied topically.

The antioxidant potential of inulin varies depending on the source.

This ingredient is also pretty picky about pH; it performs best at pH 6.5 or below.

At the right pH level, sorbic acid is "active" and can slip through the outer wall of a microbe. Once inside, it turns the cell's interior more acidic to shut down the microbe from the inside.

The EU caps this ingredient at 0.6% while the CIR has concluded it's safe at concentrations up to 1%. It's most often used around 0.05-0.2% in cosmetics.

Though this ingredient is considered low-sensitizing and well-tolerated, a very small number of people may have a contact allergy to it. Be sure to patch test if you have a history of allergies towards preservatives.

Either way, you're getting water + a cocktail of minerals and trace elements (like magnesium, calcium, potassium sodium, etc).

Officially, COSIng recognizes this ingredient as a humectant that holds and retains moisture, and solvent that helps dissolve other ingredients.

The claims about this ingredient come from its minerals. A 2025 systematic review found that seawater-based therapy showed moderate effectiveness at reducing atopic dermatitis severity and improving skin barrier function.

It also showed favorable safety profile and very minimal adverse effects.

The underlying studies pointed to improvements in stratum corneum hydration, lower transepidermal water loss (TEWL), and a healthier microbial balance.

Much of this benefit is actually attributed to magnesium: a 2005 study found that bathing in a magnesium-rich Dead sea salt solution improved skin barrier function, boosted hydration, and reduced inflammation in atopic dry skin.

It's worth nothing most of this evidence comes from bathing/soaking protocols and mineral-rich waters like the Dead Sea (not necessarily a few drops on an ingredient list).

Overall, this is a gentle, well-tolerated, water-phase ingredient that can offer light hydration and a little mineral boost.

The only caveat is that very high salt concentrations can be drying for already-dry skin.

Carotenoids and Vitamin E help nourish your skin's natural barrier. This barrier protects your skin and is responsible for firm skin.

Topically applied tocopherol has been shown to protect against UV damage by ramping up the skin's own natural defense enzymes.

It also acts as a skin conditioning agent; some studies show that regular topical use can improve the skin's water-binding capacity over 2-4 weeks.

This ingredient is especially loved for being a team player. When combined with Vitamin C, the photoprotective effect of both ingredients roughly doubles and the combo also helps reduce UV-induced DNA damage.

This ingredient has some brightening potential but it's more of a prevention ingredient than spot-fader. Cell studies show it can slow down melanin production but it's worth noting that it's not the most powerful brightener out there.

In formulations, it also serves as a stabilizer that helps protect other oxidation-prone ingredients from degrading.

Concentrations usually range from 0.1-1% in most leave-on products.

The reason this ingredient is so effective is because it forms a thin film on the skin that reduces transepidermal water loss (TEWL) while supplying linoleic acid to the stratum corneum to improve barrier strength.

The high linoleic acid content is particularly noteworthy for acne-prone skin.

Research suggests that acne-prone skin tends to be deficient in linoleic acid in sebum. Topical application may help replenish this to support a healthier follicular environment and less comedone-promoting sebum.

One randomized study found sunflower seed oil preserved skin barrier integrity in adult volunteers with and without atopic dermatitis (outperforming olive oil).

This ingredient is well-studied, gentle, and an effective emollient suitable for most skin types.

On fungal acne: This ingredient may not be Fungal acne (Malassezia folliculitis) safe. This is because it contains fatty acids with carbon chain lengths in the C11-C24 range.

Interestingly, the size of the molecule affects its behavior:

Some clinical evidence links low molecular weight versions to improved wrinkle depth, elasticity, anti-inflammatory effects, and barrier repair.

Many serums use a blend of both weights so you can get surface hydration plus longer-lasting and deeper effects.

You'll typically see concentrations between 0.1-2% for this ingredient.

Xanthan gum is a pretty common and great ingredient. It is a natural, non-toxic, non-irritating ingredient that is also commonly used in food products.

Industry-reported use ranges from 8% in rinse-off products and 2% in leave-on formulations.

A British study found lauryl glucoside to cause skin sensitivity for some people. We recommend speaking with a professional if you have concerns.

Other names for this ingredient include "Lauryl Polyglucose", "Lauryl glycoside", and "D-Glucopyranoside".

This ingredient can be derived from palm oil, or coconut oil. It is also naturally found in certain species of organisms.

According to the NOAA, this ingredient can cause skin sensitivity with prolonged use. However, this warning is taken from the Coast Guard and no studies have been done on this in relation to cosmetics.

Tridecane is not water soluble.

For instance, Habanolide is a proprietary trade name for a specific aroma chemical. When used as a fragrance ingredient in cosmetics, most aroma chemicals fall under the broad labeling category of “FRAGRANCE” or “PARFUM” according to EU and US regulations.

The term 'parfum' or 'fragrance' is not regulated in many countries. In many cases, it is up to the brand to define this term.

For instance, many brands choose to label themselves as "fragrance-free" because they are not using synthetic fragrances. However, their products may still contain ingredients such as essential oils that are considered a fragrance by INCI standards.

One example is Calendula flower extract. Calendula is an essential oil that still imparts a scent or 'fragrance'.

Depending on the blend, the ingredients in the mixture can cause allergies and sensitivities on the skin. Some ingredients that are known EU allergens include linalool and citronellol.

Parfum can also be used to mask or cover an unpleasant scent.

The bottom line is: not all fragrances/parfum/ingredients are created equally. If you are worried about fragrances, we recommend taking a closer look at an ingredient. And of course, we always recommend speaking with a professional.

There are a very small number of reported cases of contact dermatitis in cases linked to wound-care creams used over compromised skin (rather than skincare).

Overall, this is a well-studied and low-risk preservative just doing its job.

Typical concentrations run up to 0.6%, which is also the maximum amount permitted under both EU CosIng regulations and US FDA guidelines.

However, this exfoliating effect only happens at high concentrations (20%) which can be hard to find in cosmetic products.

Due to this, citric acid is usually included in small amounts as a pH adjuster. This helps keep products slightly more acidic and compatible with skin's natural pH.

In skincare formulas, citric acid can:

While it can provide some skin benefits, research shows lactic acid and glycolic acid are generally more effective and less irritating exfoliants.

Most citric acid used in skincare today is made by fermenting sugars (usually from molasses). This synthetic version is identical to the natural citrus form but easier to stabilize and use in formulations.

Read more about some other popular AHA's here: