Sensitisation vs. Sensitive Skin

Many people believe they have sensitive skin when in actual fact what they’re experiencing is skin sensitisation. Both conditions can visually look alike, may feel alike and behave alike – however, there is a key difference – one can be intelligently avoided and the other is a lifelong condition in need of continual management.

During the course of this article, we will investigate and explain the differences between sensitive skin and skin sensitisation, how skin can be healed from sensitisation and how to avoid skin becoming sensitised.

The difference between sensitive skin and skin sensitisation

Akin to dehydrated and dry skin, sensitive skin and sensitised skin are 2 completely different experiences. Take dehydrated skin as an example; a dehydrated skin condition can strike any skin type whether a person has dry, normal or oily skin. This is because dehydration is a temporary state of being and not a skin type.

The same is true for sensitised skin. A sensitised skin type is sensitive only when exposed to specific skincare ingredients/fabric dyes/laundry detergents or similar. A sensitised skin type does not show a general and chronic sensitivity reaction, however, is flared by the use or contact with specific materials. In contrast, a sensitive skin type is genetic and most likely experienced since birth. Sensitive skin types are indiscriminate and will, in general, be reactive towards any kind of change.  

Bottom line: All skin types may suffer from skin sensitisation at any age, whereas only sensitive skin types may suffer from general, persistent and indiscriminate sensitivity.

What is a skin sensitiser?

A skin sensitiser is an ingredient with the ability to activate a person’s immune system. Skincare is designed to absorb into skin, therefore, it’s important the ingredients used in skincare are skin-identical, skin similar or skin unreactive. The major difference between a skin sensitiser and a non-reactive skincare ingredient is a skin sensitiser’s ability to react with epidermal proteins.

In general, dermatologists and scientists believe a skin sensitiser is an ingredient with;

  • Small molecular weight, allowing it to easily penetrate a person’s skin barrier i.e. < 500 Daltons1
  • Has the ability to react with skin proteins to form a larger molecule
  • Is recognised by the skin’s immune function (when reacted with skin proteins) as a potential danger

 

When a skin sensitiser has bound with a ‘carrier’ protein it forms what’s referred to as an antigen2 i.e. an ingredient with the ability to cause an immune response. Skin’s immune function (langerham cells) then acquires and processes the sensitiser-modified carrier protein moving from the epidermis to the draining lymph node. Following this the antigen is presented to naive/new T-cells (a type of white blood cell/immune cell). The human body then makes T-cells specifically with the ability to recognise the new sensitising antigen and circulates these throughout a person’s body. Once this process occurs fully – sensitisation has officially been induced.  Scientists call this the induction phase.

When a person is next exposed to the same sensitiser or a similar sensitiser, the resulting carrier protein is immediately recognised by circulating T-cells and a sensitisation reaction entails i.e. skin becomes inflamed, red, angry, itchy, bumpy, hot and irritated. Scientists call this the elicitation phase.

Note: A person may be exposed to a sensitiser many times before a sensitising reaction is induced. This can cause confusion over which skincare product or lifestyle change is the root cause of a skin reaction. For example a new skincare product containing a known sensitiser could be used many times before a sensitisation reaction is provoked. Once the elicitation phase is activated a person will experience skin sensitivity whenever skin is exposed to the sensitising ingredient.

Common sensitising ingredients used in skincare

In all cases of a suspected sensitisation reaction the first step should be removal of all skincare products containing known sensitisers. While many people will be ok using these ingredients, sensitised skin types are not.

Some of the most common and known sensitisers used in cosmetic products include;

  • Hydroquinone3 – often used in skin lightening products
  • Benzocaine4 – local anaesthetic which can be found in after sun products
  • Formaldehyde – and therefore formaldehyde releasing preservatives i.e. imidazolidinyl urea, diazolidinyl urea and DMDM hydantoin
  • Paraphenylenediamine5 – used in hair dyes
  • Limonene – a fragrance ingredient
  • Eugenol6
  • Cinnamaldehyde
  • Isoeugenol
  • Hexylcinnamaldehyde
  • Citral
  • Methyl-chloro-isothiazolinone/methyl-isothiazolinone (MCI/MI) – a preservative

Frequency of exposure is a risk factor in the development of a sensitised skin condition. Therefore, to avoid sensitisation or to reduce a person’s risk of sensitisation would mean avoiding skincare products containing the above list of ingredients.

How can you prevent skin from becoming sensitised?

There are 3 key ways in which a skincare ingredient can cause damage to skin – by being an allergen, a sensitiser or an irritant. Skincare products containing a mixture of all 3 can synergistically exaggerate a skin sensitisation reaction. The first step towards a sensitiser being able to complete the induction phase of sensitisation is the prerequisite that it must travel across a person’s intact skin barrier.

The function of skin is to prevent allergens, irritants, sensitisers, bacteria and more from being deeply absorbed. When skin is forced into a trauma state, say for example by exposure to an irritant, a person’s skin barrier health is reduced, skin barrier function is lessened and therefore sensitisers may more easily be absorbed.

Studies show that when a known irritant i.e. sodium lauryl sulphate (SLS) is applied to skin at the same time as a known sensitiser in small amounts – the resulting sensitisation reaction is amplified7. Some sensitisers are also known irritants and therefore may be able to cause extreme sensitisation reactions.

Sodium lauryl sulphate is a known irritant and cleansing ingredient. SLS causes irritation by firstly dissolving away skin’s protective lipid barrier and secondly by causing denaturation (a change in shape) of skin cells. Essentially SLS is therefore able to lessen skin’s barrier properties by interfering with skins normally tightly packed ‘brick and mortar’ structure.

SLS is commonly used in dermatological tests to purposefully irritate skin so pacifying active ingredients may be tested for efficacy. SLS is also commonly found in skincare products such as shower gels, bubble bath, face wash and exfoliating products. Therefore skincare products containing, for example, a combination of an irritant and a sensitiser i.e. SLS and imidazolidinyl urea have greater potential to cause sensitisation reactions in the end user.

Bottom line: The best way to avoid skin from becoming sensitised is to craft a protective skincare routine which respects and builds upon the skin’s own barrier properties.

How to protect skin against sensitisation

Sensitisation can be life changing as many known sensitisers can be commonly found in cosmetics, laundry detergents and cleaning products. Exposure may be controlled within a person’s home however environmental exposure i.e. at the home of family or friends, or during a holiday is largely not under a person’s control. Therefore protecting skin against sensitisation is an important care practice.

The best ways to protect against sensitisation include;

  • Avoidance of SLS
  • Avoidance of irritating skincare products
  • Use of mild cleansing products i.e. griffin+row Cleanse skin cleanser
  • Daily use of sunscreen – the best would be a mineral based sunscreen
  • Avoidance of common sensitisers such as citral
  • Avoidance of strong smelling/fragranced personal care products
  • Use of barrier building moisturisers i.e. griffin+row Enrich
  • Use of sensitive skin friendly skincare products
  • Keeping showering and bathing time to a minimum
  • Showering and bathing in warm not hot water
  • Using softened water for bathing/cleansing
  • Use of pH balanced skincare products
  • Avoidance of soap/high pH cleansers

An intact and healthful skin barrier relies on a few simple factors;

  1. An oil based lipid barrier
  2. Tightly packed skin cells
  3. A healthy acid mantle with pH of between 4.2-5.68

Therefore skincare which protects respects and helps to maintain these factors will also help to protect against skin sensitisation.

 

How to heal sensitised skin

What should a person do when skin has suffered a sensitisation reaction? How can sensitised skin be healed? Once skin is sensitised will skin always be sensitive?

Although sensitive skin and sensitised skin are 2 completely different conditions, once a sensitisation reaction has occurred or is in full swing, the changes needed to help skin heal are similar. However with one difference – sensitised skin can only be helped to heal after the sensitising ingredient is identified and eliminated.

Step 1: Remove use of all sensitising ingredients i.e. skincare, laundry detergents and personal care products.

Patch testing performed by a dermatologist or hospital can help reveal the specific ingredient responsible for sensitisation, however, the quickest and perhaps easiest way to begin treatment is to remove all known sensitisers from a person’s daily routine.

Step 2: Reduce inflammation.

Sensitisation reactions involve activation of a person’s immune function which therefore triggers inflammation. When inflammation is lessened the sensitisation reaction will be reduced and therefore skin can begin healing.

Inflammation may be reduced by;

  • Use of anti-histamines
  • Use of anti-inflammatory/protective skincare

Examples of anti-inflammatory/protective skincare ingredients include: colloidal oatmeal, bisabolol, allantoin, zinc oxide (a registered FDA skin protectant), calalmine, niacinamide, evening primrose oil.

Step 3. Use of sensitive skin friendly skincare.

While skin is sensitised a person’s skin barrier function is reduced and therefore may be easily irritated by any number of cosmetic ingredients. It is therefore best to use a simple, sensitive skin friendly routine. Skincare products should be free from fragrance, use soothing active ingredients, be pH balanced and free from SLS.

Step 4. Avoid future contact with identified sensitiser.

Once skin has become sensitised to a specific ingredient and has progressed through the induction phase of sensitisation i.e. T-cells which recognise the sensitiser have been introduced into a person’s immune function, future contact with the activating sensitiser will cause swift reaction. This is often what causes people to believe they’ve developed a sensitive skin type. However, treating skin sensitively will not help relieve symptoms unless the causing sensitiser is avoided.

Another factor which causes confusion is the induction phase of sensitisation may take significant time to complete. This means skincare products may be used for days, months or even years before causing sensitisation. However, once the induction of sensitisation is complete, whenever the causing ingredient is used a quick and aggressive sensitivity reaction will occur.

How to tell the difference between skin sensitisation and sensitive skin

When understanding whether a person is experiencing sensitisation or sensitive skin, a few simple questions can usually identify the culprit. These questions are based around understanding if a person has always had sensitive skin or whether perceived sensitivity has been induced by a sensitiser.

  1. Did sensitivity occur after using/recently introducing a new skincare product?
  2. Have you always had a sensitive skin type?
  3. Does your mum/dad/sister/grandparents have sensitive skin? Do eczema or allergic conditions run in your family line?
  4. At what age did you begin experiencing skin sensitivity?
  5. Have you used active skincare ingredients i.e. salicylic acid/glycolic acid, retinol and vitamin C/ascorbic acid with no previous issues?

Yes to questions 1 and 5 points towards a sensitisation reaction as the person in question does not have a classically sensitive skin type.

Yes to questions 2 and 3 points towards a person having inherited a genetic predisposition to a sensitive skin type.

The answer to question 4 will add weight to either diagnosis. If a person began to experience sensitivity from a young age or during times of hormonal imbalance/hormonal change – then the likelihood is they’re suffering from a sensitive skin type. However, if the answer is that they only experienced sensitivity in adulthood, then it’s likely that they have sensitisation.  

Sources and references
  1. Skin irritation and sensitization: mechanisms and new approaches for risk assessment. D. Basketter, R. Darlenski, J. W. Fluhr Skin Pharmacol Physiol. 2008; 21(4): 191–202. Published online 2008 May 29. doi: 10.1159/000135635

  2. Determinants of skin sensitisation potential. David W. Roberts, Aynur O. Aptula, J Appl Toxicol. 2008 Apr; 28(3): 377–387. doi: 10.1002/jat.1289

  3. Determinants of skin sensitisation potential. David W. Roberts, Aynur O. Aptula, J Appl Toxicol. 2008 Apr; 28(3): 377–387. doi: 10.1002/jat.1289

  4. Skin sensitization–a critical review of predictive test methods in animals and man. P. A. Botham, D. A. Basketter, T. Maurer, D. Mueller, M. Potokar, W. J. Bontinck, Food Chem Toxicol. 1991 Apr; 29(4): 275–286.

  5. https://osha.europa.eu/en/tools-and-publications/publications/factsheets/40

  6. https://www.ecetoc.org/wp-content/uploads/2014/08/ECETOC-TR-077.pdf

  7. Determinants of skin sensitisation potential. David W. Roberts, Aynur O. Aptula, J Appl Toxicol. 2008 Apr; 28(3): 377–387. doi: 10.1002/jat.1289

     

  8. Blank HI, Measurement of pH of the skin surface. J lnvrsl Dermatol 1939;2:67-79.